Indi an Jou rnal of" Chellli stry
Vol. 45A. Oct ober 2006, pp. 2 1 7~2 1 85
-
The quantum chemical investigation of the addition reactions of Br2 to
homocubylidenehomocubane and its derivatives
Rl za ;\ bbasog lu '" & Scvil
Sava ~ kal1
ytlmaz
Depa rtm ent ur Chelni stry . Fac ult y o r Science. K~lrad e ni z Technical University, 61080 Trabzon. '!'urkey
Elllai l: rabbas@ ktu. edu .tr(RA): sev il y@ klu .edu. tr(SS)
i?eceil'ed // /\ pril 2005 ; rerel'iseri 2 AIIg II.l1 2006
Th e elec tro ni c and gco lllciri c stru ctures or hOllloc uby lidenchollloc ubanc ( HC). 11'1111.1- ( l - meth y l-2-hollloc ubyli dcn)- I Illcth y lhornoc ubane ( DM II C) and I mlls-( 1-lerl -but y l-2-homoe uby lid cn)- I-lert-bu ty lhollloc ubanc ( D13HC) lIlolec ules
ha ve been in\'cs ti gated by 13 3L Y I'/6-3 11 G* Illc th od. Th ese resuit s ,Igree with X-ray resuits and show that th e doubl e bond or
HC 1Il0iec uie has :l planar structure. w hile th c double bond s in DMHC and DI3HC molecule arc :l lmost planar. The
co mpl exes ( I : I 7r comp lexes) or the molec ul es w ith 13r ~ have bee n in ves ti g:lted by B3L YP/6-311 +G * met hod and it is
obse rved th at th e stable co nl'igu rati ons ha ve an ax ial stru cturc. Th e elec tro nic and th e steri c ractors arfecting th e stru cturc
and th e st:lb ilit y or th e molec ular comp lexcs ha ve becn studied. it is observcd that the DMIIC ... I3r ~ co mplex is more stable
than II C .. . 13rc co mplex. 'rh e DI3HC ... l3rc co mpl cx con taining th e bulk y l ert -buty l group has stabilit y o r steri ca lly
enculllbered olerin-brom co mpl cx :lnd it depends on th e naturc or 'cage' substitu cnts on th e double bond ca rbons. The
brid ged brom onium c;l ti on is th e more siable cati on among th e cation ic intermediat es rorilled in th e addition reacti on of
bromine to HC and th e reaction occurs via this clIion. Th e nu cleo phili c attack by bromide ion is not steri ca ll y preve nted to
1-IC-l3 r+ bridged bromoniulll cat ion and as a result , normal 9. 9'-dibrolllide product is rormed. Th e nuclcophili c attack by
bromide ion is steri ca ll y pre vc nted to AD-l3 r+ bridged bromo nium ca ti on.
Elec trophilic halogenati on of olerins is one or th e
class ical reacti ons in organic chemistry and have been
studied exten si ve l y theoret icall y and ex peri menta II y 1· 17 . H owever, tIl e Illec Ilanl' sm 0 j' tIli' S reacti.on as
well as the nature, the stru cture and th e stab ility of th e
reacti on intermediates is still under di scuss ion. In
ord er to anal yze the reac ti on mechani sm and stereochemi stry, detail ed data about th e structures and
stabiliti es or th e intermediates such as olefin-hal ogen
molecular complexes ane! ca ti ons formed durin g th e
reactions arc needed. Ol efin-hal oge n molecular
complexes arc important intermediat es rormed in th e
earli er steps of thc addition reacti on l . Since th e
interm eckltes ha ve low stabiliti es ancl high reactivities, it is dirricult to obtain inrormati on about th eir
stru ct ure and th e stability ex perimentally . In ract,
quantum chcm ica l calculations mi ght help in
ob taining of detailed inrormation about the stru cture
and stability of interm ed iates.
Addition reactions or halogens to unsaturated
strain ed molecule and th e reac ti on intermediates have
been quantum c Il eml. ca IyI 'Inves tl.ga tec11 .71O.1~
.
. We
have recentl y reported th e th eoreti ca l investigations
on the additi on o f bromin e and chlorine to olcl'ins
. I n.glc
. I structure'15·17 .
Wltl
t
).
The elec trnphili c addition reac ti on o f Br2 molecul e
to steri cally encumbered homocubylideneholllocubane (HC) ha ving 'cage' stru cture and its derivati ves ha ve been in ves ti gated experimentall y. It has
bee n determined that normal dibromide product is
form ed in th e addition reacti on I S. Due to th e inherent
sy mmetry in homocubylideneholllocuban e, it is not
poss ible to deduce the stereochemi stry of electrophilic
addition (i .e. , sy n or anti) across th e C=C double bond
from only knowledge of th e structure of the adduct.
Hence, determi nation of th e structure and th e stabi I i ty
of th e intermed iates formed in the addition reac ti on is
important. On the other hand , although th e normal
dibromide addition product is rormed in th e bromi nation reaction of HC molecule, the bromination or
sterica II y
encumbered
adamanty I i deneadaman tan
(A D) cannot proceed beyond th e stage of th e
bromonium ion I t). In ex plainin g th e structures or th e
cation, intermediates form ed in th e bromination of
each olefin is important. Mainl y th e stru cture of the
olefin determines the stabilit y of th e complex and the
in termed i ates.
In thi s study , th e geometry and th e elec tronic
structure of homocubylidenehomocubanc (HC), [ mlls ( I-meth y l - 2- homocuby I iden) -\ - mcth y IhOlllocuball e
I DIAN J C HEM, SEC A, OCTO !3 ER 2006
2 180
(DMHC) and trans-(l-tert-butyl-2-homoc ubyliden)- Itert-butylhomoc uban e (DBH C) molecules (as shown
in Scheme I) have been in ves ti ga ted by DFT method.
Olefin-Sr2 molec ul ar com plexes have been stud ied
using DFT method. The relati onsh ip between the
qu an tum chemi cal parameters of olefin s and the
stab ili ty and pro perti es of molecul ar com plexes have
also been stu died. Also, th e splitting of HC. .. Br2
molec ul ar co mpl ex res ults in th e formin g of cyclic
three-membered bro monium ion (HC- Br+) and its
iso mers geo metri c and elec troni c propert ies have been
in ves ti gated by ab initio meth od. The geo metri c
parameters of HC-Bt and AD- Br+ bromo nium ions
have been co mpared .
Bas is-set superpOS Iti on error (BSS E) energies are
co rrec ted. The stru cture and the stab il ity of cyc li c
three-membered bromonium ion of (HC-Br+) and its
iso mers were in ves ti gated by HF/6-31 1G*( ref. 23)
meth od. All stati onary po ints were characteri zed by
calcul ating th e vibrati onal freqency Lind ze ro poin t
vibrati onal energies were added for al l spec ies. Full
geometry optimizati on was ca rried ou t empl oy ing th e
Polak-Ribi ere (co nju gate gradi ent) al gorithm (co nvergence of 0.0000 1 kcal mor l ) and an RMS gradi ent at
0. 00 I kcal (A mol)" ' . The calcul ati ons were perfo med
with HyperCh em 7. S and Gaussian98 program with
an IBM PC Pentium IV co mput er.
Full geo metri c optimi zati ons of HC molec ul e and
its deri vati ves (DMH C, DBHC show n in Scheme I)
were done by B3 L YP/6-3 11 G* meth od and the
structure of th e molec ul es were also inves ti gated in
detai I (Fig. I). The total energy (£",,), the energies
(C II OMO and ELUMO) of fron tal molecul ar orbitals, the
doubl e bond length (rc=c) of each molec ule, the
di stan ce (rl l... lI ) between th e hyd rogen atoms situated
in ~- p os i t i o n s to th e dou bl e bond in diffe rent homocuba ne moieties, an d the distance (r,clI ) between
R group (Sc heme I) and hydroge n atom in the
a -pos iti ons to th e dou ble bond have been ca lcul ated.
24
The valu es of th e out-of-pl ane bendi ng angle (X) of
eac h molecul e we re calculated acco rd ing to th e res ults
of B3L YP/6-3 1 I G* calcul ati ons to determin e th e
st ru ctural deform ation of double bond. The vo lumes
of R gro ups25 were also calcul ated. These res ul ts arc
given in Table I.
Methodology
The geo metry and th e elec troni c stru cture of th e
HC molec ule and its derivati ve (DMHC, DBH C)
(S cheme I) were investi gated by th e DFT meth od at
th e B3L YP/6-3 11 G"' [20, 2 1] level. The th eo reti cal
in ves tigati on of 0lefin-Sr2 molecul ar co mpl exes was
performed by using th e B3 L YP/6-3 11 +G* meth od 22 .
HC( I)
DM HC(2)
D!3HC(3)
R= H
R = C H,
R = C(C H,),
Schcmc I
2
1
3
Fi g. I- The optim ized geometry o f th e investigat d mo lec ul es by the !33L YP/o-3 1I G* lllethod.[ HC (I ); DMHC (2) ~lIld D!3HC (3)1.
Tab le I- T he ca lcu lated IOtal e ne rg ies (hartree), th e e ne rg ies of fro nti e r mo lec ul ar o rbi ta ls (eV), th e do uble bo nd I ng th s (A), th e
d ista nces be twee n the hydrogen atoms in the B- pos iti o ns (A), th e d is tances betwee n the R g ro up a nd the hydroge n a tom in the
a-posit ions (A) , th e o ut-of-p la nc be ndi ng a ng le (deg) (!33L YP/6-3 1 IG*) and th e calc ul ated vo luilles (A 3) o f R s ubsti tuen ts
V
Mo lecu le
Po int groups
£101
CIIOMO
CLUMO
rc=c
1'11. ... 11
r IL .. 1I
X
2.520"
h
2.288
h
2.005
0.000
71.7
0.0 10
150.3
0.0 15
3 11. 3
He
D ~h
-694.929
-6.203
0.308
1.332
5.56 1
DMHC
C~h
-772.565
-6.1 54
0.348
1.338
5.580
DLlf-iC
C"h
- I005.444
-6. 126
0.356
1.348
5.646
" Distances be tween the hydroge n a to ms in the a-posi tions.
Average distance between a -hydrogen and hyroge ns o r R group.
h
Al3l1ASOGLU & Y ILM AZ: ADD ITI ON RE ACT IONS OF l1r~ TO HOMOCU13Y LlO ENE II OMOCUBANES
218 1
(th c C n axis o f th e [3r2 molecul e is perpendicula r to
th e plan e of doubl e bond) and equatori al (thc C r. ax is
o f Br2 is parall el to th e plan e of doubl e bond)
pos iti on s. By con siderin g th ese, th e full geo met ri c
optim izati on of the vari ous co nfi gurati ons of
HC. .. Br2, OMHC. .. Br2 and OBH C .. . Br2 sys tems wc re
perform ed and th e stabl e configurations corrcsponding to th c minimum energy were determin ed. Br::>
molec ul e is in axial positi on to th e double bond plane
of olefin in th e stable confi gurati on correspondin g to
th e minimum energy of the IT-complex for each
sys tem . Th e opt imi zed geo metri es o f th e molecular
complexes are gi ve n in Fig . 2. The stabili zatio n
of
the
mol ecular
co mpl exes
encrgies
Results and Discussion
The B3L YP/6 -3 11 G " results show that although
there arc bulk y 'eagc ' groups attached to th e doubl e
bonded carbon s in HC molecul e, th e ca rbon-carbo n
double bond has esscntiall y a planar stru cture and th c
point group of the molecul e is 0 211 . Th ese rcsults arc
in full agrecment w ith th e ex perim ental X-ray
ls
results . Th e s urro undin ~ of th e double bond in
2
OMHC and OBH e ' mol ~cul es is ;t1m ost planar and
thc molecul es ha ve C211 point group . Th e doublc bond
di stance, (rc=c), and th e di stance, (rl1. 11) between
hydrogen atoms situ ated in ~ - po s iti o n s in crease with
increas ing vo lumc o f R group (Tabl e I ). On th e oth er
hand, HOMO energy le ve l of th e mol ec ul e increascs
and th e ion izati on potential (I P=- f:llm10) dccreases
w ith increasing clec tron donor propert y o f R group as
show n in Tabl e I . Thu s, th e ioni zation potcntial s o f
molecules 1-3 (Schcme I ) decrcase and th c electrondonating abilit y incrcases with respcc t to R group .
In ord er to determin e th e structure and the stability
of HC. .. Br::>, OMHC. .. Br::> ( II ) and OBHC. .. Br::> (III)
molecu lar comp lexes ( I : I IT-complexes), 0lcfin-B r1
sys tems wcre inves tigat ed in detai l at B3L YP/63 11 +G * level. It is poss ibl c that th e brom ine mol ecu le
approaches to the doubl e bond of the olefin In axial
(L1E = ( E,,,,,,. + Ell" )- ElI/oI _II"
) ,
the equi librium di stance
R X. l1r (X is midpoint of th e C=C bond of olefins), th e
di stance (rI LH) betwce n th e hydrogen atoms in th e
~-position s of the double bond , in the different
homocubane moicty, the distance (rIL II) between R
group and hyd rogen atol11 in a-pos iti ons and th e other
ca lculated properti es are given in Table 2. The oUf-ofplane bending angle (X) of the comp lexes in olctins
have been al so calc ulated accord ing to th e results of
B3L YP/6-3 1 I +G * method (Table 2).
111
II
Fig. 2- T he optillli zed geometri es of HC. .. l3r2( I). OM HC. .. Br2 (II ) and 013HC ... I3r2(1II ) molecular co mplexes by th e B3L YP/6-3 11 +G '"
meth od.
Table 2- Th e properties of , HC ... Br2 ( I). OMH C ... l3r2 ( II ) and OBHC .. . l1 r2 (II I) molecul ar co mplexe s (B3L YP/6 -3 11 +G ';' ).
(Gcomclri c parameters are in A ; th e out -of-plan e bending an gle is also in dcgrce unit. )
M olecular
co mplex
a
/1./:'
(kca l/ mo l)
N X-Br
r Ur -1l1
Tran sferred
charge olefin s to
13 r2( e)
Charge on bromines. (e)
nca r
far
1'11. 11
I'R II
X
\.,
2.6 1
2.9 1()
2.375
0.0-17
0.02 1
-0.068
0.038
2.5 16
8.42
10. 883
II
8.0-1
2.8-10
2.377
0.0-19
0.020
-0. 069
6.070
2.34 1
8.86
10. ( 33
III
5.8-1
3. 173
2.37 1
0.032
0.0 10
-0.048
5.95 1
2.{){)4
5.08
10.805
= HOM O"II- LU
~O hrom energ.y
gap.
INDIAN] CHEM, SEC A, OCTOBER 2006
Electron transfer from olefin to the bromine
molecule is observed in each complex. For that
reason, bromine in the charge transfer complexes
(CTC) is partiall y polari zed. The bromine atom near
the doubl e bond has a parti al posi tive charge and the
oth r bromine has a partial negati ve charge (Table 2) .
The DMHe. .. Br2 (II) complex have the larges t
stabilization energy and the smalles t equilibrium
distance among the molecular complexes, i.e., DMHC
makes the most stable mol ec ular eomplex with Br2
mol ec ul e compared to HC and DBHC molecules.
DBHe. .. Br2 (JIJ) mol ecular complex is more un stabl e
than He. ..Br2(1).
]n order to make these res ults clear, ii: is important
to determin e the electronic and steri c factors affecting
th e formati on of the molec ular comp lexes . According
to th e frontier mol ecular orbi tal theory , the formation
of olefin-bropline molecular comp lex occurs when the
HOMO orbital of olefin (donor) and LUMO orbi tal of
bromine (acceptor) mutually interac t26 . For effectiv e
and optimal HOMOoll- LUMObrolll interaction, it is
necessary th at the energies of the orbitals are close
and HOMOoll- LUMObrolll energy gap is small. Consequentl y, the electron-donating ability of olefin (ionizat ion potential value, IP = - CIIOMO) is im . ortant in the
formation of olefin-bromine molecu lar co mplex. The
electron-donor groups (R) situated in th e surrounding
of the olefin double bond enh ance HOMO energy
level of alkene 27 and affect the formation and stabi lity
of olefi n-bromine mol ec ular complexes ositively. In
oth er words, th e electron-donor groups reduce the
valu e of HOMO olf -LUMO brolll energy gap that makes
th e charge transfer to bromine from olefin easy
lead ing to increase in th e stability of olefin-bromine
co mpl ex (Table 2). Therefore, th e stability of th e
molecular complex with bromine molecu le increases
wh en the electron-donatin g ability of o lefin increases.
That is, with respect to electronic effect, the stability
of the co mpl exes increases as: He. .. Br2 >DMHe. .. Br2
> DBH e. .. Br2' However, the electronic effect al one is
not sufficient to explain the stability of complexes.
For exa mpl e, the DBHe. .. Br2 complex containing the
bulky tert-butyl groups is more un stable than the
other two complexes, indicating th at the steric effect
should also be taken into account along with th e
electroni c effec ts in determinin g stability of the
comp lexes.
In order to achieve the optimal 0lefin-Br2 interacti on in the formation of the molec ular co mpl ex, th e
approach of bromi ne toward th e doubl e bond of olefi n
in a certain position should not be hindered stericall y.
In the HC type of mol ecules, four hydrogen atoms are
situated in ~-po s itions on both sides of the double
bond. The di stance (rl-l .lI) between hydrogen atoms
that are situated in ~-positions of the doubl e bond in
the molecules and in l1-compl exes are given Tabl es I
and 2. The di stance (rll . lI) between ~- hy drogen atoms
(hydrogen atoms situated in [3-positions) th at prevent
th e bromine molecule from approaching th e doubl e
bond in each olefin increased with th e formati on of
the complex and reached a maximum in th e stable
configuration of the l1-complex . The formation of
olefin-bromine mol ec ular compl exes w' s ac hi eved by
increasing the di stance (rll.lI) between the ~-hydro­
gens and by the pyramidalization of the doub'e bond
(Table 2). When the pyramidalization degree of the
olefins increases; their chemical reactiv iti es increase
and their steric strains decrease 28 . Th us, th e fact ors
that increase the di stance between ~-h y dro ge n atoms
and ease the pyramidali za ti on of th e doubl e bond
positively affect the formation of molecular co mplexes and increase their stability. Among th e
complexes investi gated, th e bes t doubl e bond pyram idali zation and th e largest distance (rHH) betwee n
~-hydrogen atoms is found in the DMHe. ..Br2 (II )
complex (Table 2). Methyl groups attached to the
all yl ic carbon atoms in DMHC mol ecu le affect th e
pyramidalization of the double bond in DMHe. .. Br2
complex positi ve ly and also increase the di stance
between ~-hydroge n atoms. The di stances (rILII)
between the hydrogen atoms and methyl gro ups in
DMHe. .. Br2 complex are much larger than those in
DMHC (Tables I and 2). Hence, th e steric interacti on
between methyl gro ups and the hydroge n atoms in
DMHe. .. Br2 comp lex is smaller as compared to th at
in DMHC molecule. Thu s, the electronic and steric
factors positi vely affect the formation of DM He. .. Br2
complex and the increase its stabili ty (Tab les I
and 2).
The complex undergo ing the least struct ural
defo rmation of th e doubl e bond is DBHe. .. Br2
co mpl ex (Table 2). The di stances (rR ..H) between
a-hydrogen atoms and tert-butyl groups in th e
complex and in the molec ul e are almost th e samc
(Tabl es 1 and 2) . Hence, th e strain caused by th e
interacti on between hydrogen atoms and tert-butyl
groups in DBHC molecu le is not lowe red mu ch in the
DBHe. .. Br2 complex. Thcrefore, the bulky tert-butyl
groups protect th e doubl e bond in DBHe. .. Bre
syste m, making th e olefin inert towards th e addition
AI3I3ASOGLU & YILMA Z: ADDIT ION REA CTIO NS OF Br2 TO HOMOC UBYLIDENEHOMOCUBAN ES
n
2 183
111 (rotated 90°)
Scheme 2
+
+
AD---Br
NK---Br
Schcmc 3
Table 3- The calcul ated cc ntral C-C bond lengths (rc-d . th e C- l3r bo nd lengths (rC-I3,.) . th e di stan ces betwee n th e hydrogc n ato ms in
th e Cl-pos iti() ns of the ce ntral bond , in the different cage mo iety (r " 11. .. 11) , the di stances between the hydrogen ato ms in th e P- positions
( r 1\ 1. .. 11), th e dia go nal di stan ces betwee n the Cl - and P-hyd roge ns (N,,) and the dia go na l di stan ces between the P- and P-hyrogc ns (RII ) .
(Th t: geoillctri c parametcrs are in A) (1-IF/6-3 1IG *)
I3rolllonium cati on
Point gro uJls
rc-c
rC· IJ ,.
r u 11. .. 11
r ll 11. .. 11
R"
RII
AD- l3r+
C 2v
C2v
1.484
1.445
2. 167
2.1 49
1.993
2.5 15
2. 155
3.72 1
3.258
4. 052
3.339
4.558
HC- l3r+
" The X- ra y diffracti on data indi cate that th e brollloniulll io n of AD-Br+ is esse nti all y sy milletri ca l with the fo llow ing avcraged
stru ctural pa rameters rc-c 0= 1.49(ii.) and rc.IJ,.=2. 11 (A) (re f. 29).
2 184
IN DIAN J CH EM. SEC A. OCTOB ER 2000
react ion. Th ese groups al so preve nt th e optimal
interacti on or brumine molec ule w ith th e doubl e bond
in 7I-co mplcx and red uce the stab ility of th e co mpl ex.
The polarizati on or bromine and subsequentl y th e
heterol ytic splittin g or HC" Br2 molecular co mpl ex
results in th e rormati on of cyclic three-me mbered
bromonium ca ti on (HC-Br+). Thi s ca ti on and its
isomers are th e predicted ca ti oni c intermeciiates or th e
addi ti on reac ti on (Scheme 2) . In ord er tll determine
th e stru ctures and relati ve stabiliti es or th e cati ons,
their full geometry optimi zati on has bee n performed
by HF/6-3 11 G * method . Th e elec tron ic properties ~lIld
th e geometri c parameters ha ve been cal culated.
Th e mos t stabl e catio n amo ng the in ves ti gated ions
(Scheme 2) by using H F/6-3 11 G " meth od is th e
cyc lic three-m embered bromonium cation ( I). Aceo rding to HF/6-3 11 G" meth od, cati ons (II ) and (II I) are
4.228 kcli/mol and 8.074 kcal/mol less stabl e than
cat ion (I), res pec ti ve ly. Th e ioni c addition or bromin e
to homocubylidenehomocuban e is pred icted to
proceed via th e cyc li c three-m embered bromonium
ion ( I) (cati on I-B f co uple is ass umed to be in the
tran siti on form ), since thi s cation is the mos t stable
one among th e cati oni c intermed iates (Scheme 2).
However, by ana logy to th e electrophilic bromination
of adamanty lideneadama ntane, it is likely that
bromination of HC proceeds anti- stereospecifi ca ll y
via th e bromonium ion (I ). It is k nown that
bromination of HC molec ul e gi ves th e normal
dibromide addition product. The bromination of AD
molecul e cann ot proceed beyond th e stage of th e
cyc li c three- membered bromonium ion (A D-Br+). T o
exp lain th e reason for this, the full geometric
op ti mizati on of A D -Br+ ions w as done by HF/63 1 I G* meth od and th e elec troni c and th e geometric
properties were calcu lated. Th e resu lts are co mpared
w ith those of HC-Br+ ions Crabl e 3).
The values or R" (th e diagonal di stances between
th e u- and ~ -h ydrogens ). R~ (the di agonal distances
betwee n the ~- and ~-h y droge n s) calculated by the
HF/6-3 11 G * meth od are also in agreement with each
bromonium ion as show n in T abl e 3. Th e average
va lues of R" and RII for AD-Br+ ion are 3.258 A and
3.339 A, respec ti ve ly. Th ese valu es for HC-Br+ ion
are 4.052 A and 4.558 A, respec ti ve ly. The
nucleophili c attack of th e initiall y formed bro mide ion
(Br-) on the cat ioni c ce nter o f bromonium ion occurs
rrom th e opposite side o f th e three-membered ring.
For such a nucl eophili c attack, th e average va lues of
th e cavity radii ~(} (R" and ( 11) f ormed by the hydrogen
atoms or bromonium ion mu st be large r th an th e
average va lue of th e ion radii (RBr- - 3. 64 A) or
bromide ion (Bf). Since th e average RIL and RII va lues
fo r AD" .Br+ ion are smaller than th e ave rage R 11rvalu e, in A D ". Br+ the nucleophi li c attack o f Br ion is
sterically prevented as show n in Scheme 3. Fo r th e
HC-B r+ ion, th e average RIL and RII va lues are large r
than th e av erage R Br- value, th e nucleoph ili c attack to
bromonium ion of Bf ion is no t stericall y pre vented
and normal dibroill ide add iti on produ ct is obtained.
RcI'crcnces
I
2
3
4
5
o
7
8
9
10
II
t2
13
t4
IS
Ilcl ilic i G. Chapp<.: C B ianchin i R. Lcno ir D & f-krgcs R. j
Alii Oelll Soc I 17( 1995) 1200 I.
Ikrgcs R. Allgc l\' CII CIII 1111 L'd Eligl. 3-1 ( 199 .... ) 5 1.
Rui z E, D<.:nni s R. Sa lahub R & Vela A. J 1'11\'.1 CIII'III.
100( 1996) 12265.
Brown R S. /I cc Cll ell l Ne.I , 30 ( 1997) 13 1.
Bianchini R. Chappc C L enoir D. Llllllllell It I-k rges R &
GnIIH: nbcl' J. A llge ll ' Clli'1II III! Ed Lllgi. 30( 1997) 128-1.
Bianchini R. C hi appe C Mom LG . Lenoir D. LClll lllcn P &
Go ldberg N. Cllelll Lllr J , 5 ( 1999) 1570.
Chiappc C Ruberti s A D, L <':l1l lllcn P & Le noir D. j Org
Cll elll. 65 (2000) t 273.
Lc gon A C & Thulll IVood J M A . PII."s ChoJ/ CIICII I 1'11.1'.1'. 3
(200 1) 1397.
Chi ,lppc C, Ruberti s A D. LClllmen D. Ja b,; r A. L enoir I).
Wallcuboehi C & Ponclli C S. J Org Cllel/l . ()7 (2002) 7000.
Sm ith W [3. J Org Oelll . 6:\( 1998) 266 1.
C hiappc C Ruberti s 0 A . Dctert II, L cnoir D. Wannere C &
Sc hl cy<.:r R P, OCIII £ lIr J, 8 (2002) 967.
Ratherc R, Lind cman S V , Z hll C J. Mori T . Sc hleye r R P &
Koc hi J K . J Or,!!, CII CIII, 07 (2002) 5 t 06.
L cnoir D & Chi app<.: C Clli'1II £ lIr j. 9 (20(LI) 1037.
Chiappe C. D<.:tcrt I L L cnoir D . Pamclli C S & Ru asse M F. j
Alii Cll o ll Soc, 125 (2003) 2864.
Abba sog lu R, J Mol Slnrcl ( Tlleocllelll) , 6:--:6 (200-1) I and
rcf<.:rcnces th erein .
Abbasog lll R & Y Jimaz S S. /I/(lioll J CllclII. 43A (200-1 )
2497.
17 Abbasog lu R & Y Jimaz S S, Ilidiall J Cll elll . 44A (2005) 22 1.
18 M :llchand A p. V idyasaga r V . Wat son W H. Nag l A &
Ka shya p R P. J Org O elll . 56 ( 199 1) 2R2 .
t9 Sicbocka-Tilk H. Motall cbi S.
agovski R W , Turn er 1'.
13rown R S & McDonald R. J Alii Cllclil Soc. I t 7 ( 1995)
8769.
20 L cc C, Yan g W & Parr R G, 1'11.'".1 Rei' /J. 37 ( 988) 7)55.
2 1 Ikc kc A 0 , J Oelll 1'11.".1, 98 ( 1993) 5648 .
22 Fri sc h M J. Poplc J A & 13inklcy J S, J Cll elll 1'11.1'.1', 80
( 19R4) 3265.
23 Kri shnan R. Binkley J S. Seeger R & Pople J A . J Cll elll
1'11.1'.1'. 72( 1980) 650.
24 Ermcr 0, Ik ll P & Masun S A. Allgell' Cllelll 1111 Ed L'lIgl. 28
( 1989) 1239.
25 13odor N. Gaba ny i L & Wang G. J 1\111 Cllefll Soc. II I ( 1989)
37)53.
t6
A 13 l3ASOGL U & Y ILM AZ: A DDI T ION REA CT IONS
26
27
28
Flcming I. Fro ll/in Or b i ra ls (l ilt! O rgoll ic Chelll i('a l
Reac/ioll s, ( Wi Icy U K) 2000.
HOLIk K , J ; \11 1 Cit I'll I SoC, 95 ( 1973) 4092.
Wat son W H, S/ereuc!l elll is /r\, alit! NeaCli l' i/v oj" Srs/ellls
COIl /a illill g 1f Elec/ r(}//s. (Vcrl ag Chcmi c, Florid a) 1983.
or l3r2 T O HOM OCU BYLID ENEHOM OCUBA NES
29
30
2 185
Bro wn R S, agarski R W, i3cnnct A .J. .M cCi ung R E D.
A art s G H M , Kl obllkow ski M . M cDonald R & Sant arsiero n
D , J / \11 1 Citelll Soc, I 16 ( 1995 ) 244l) .
Rath orc R, Lindcman S V , Z hll C - J. M ori T , Schlcyer P V R
& Kochi K , J O rg Chef ll. 67 (2 002) 5 106.