Page 342 - Advanced Organic Chemistry Part B - Reactions & Synthesis

314 OH OH
H O H CH 3
RO C CO H
2
2
CHAPTER 4 CH 3 CH 3
H C I , NaHCO 3 O O
2
Electrophilic Additions 2
to Carbon-Carbon H CH Cl 2 H ICH 2 H
2
Multiple Bonds ICH 2
2 87%
preferred R = H not formed
conformer R = CH 3 79%
CH 3
H I 2 , NaHCO 3 CH 3
HO CO 2 R CO 2 R
CH Cl
C 2 2
H 2 O
H ICH 2 H
preferred 3 R = H 66% only products
conformer R = CH 3 88%
On the other hand, when the competition is between a monosubstituted and a disub-
stituted double bond, the inherent reactivity difference between the two double bonds
overcomes reactant conformational preferences. 78

CO 2 – CH 3

preferred reaction site,
CH 3 regardless of conformation

Several other nucleophilic functional groups can be induced to participate in
iodocyclization reactions. t-Butyl carbonate esters cyclize to diol carbonates. 79
) CH
ICH 2 (CH ) CH CH 2 ICH 2 (CH 2 2 CH 2
2 2
I +
CH 2 CHCH CHCH CH CH 2 2 O O O O
2
2
2
OCOC(CH )
3 3
O (major) O (minor)
O
Lithium salts of carbonate monoesters can also be cyclized. 80
ICH 2 CH ICH CH
1) RLi I 2 3 2 3
CH 2 CHCH CHCH 3 CH 2 CHCH CHCH 3 O O +
2
2
2) CO 2 O O
Li
OH OCO – +
2
O
(major) O (minor)
Enhanced stereoselectivity has been found using IBr, which reacts at a lower
temperature. 81 (Compare Entries 6 and 7 in Scheme 4.4.) Other reagent systems that
generate electrophilic iodine, such as KI +KHSO , 82 can be used for iodocyclization.
5
78 M. J. Kurth, E. G. Brown, E. J. Lewis, and J. C. McKew, Tetrahedron Lett., 29, 1517 (1988).
79 P. A. Bartlett, J. D. Meadows, E. G. Brown, A. Morimoto, and K. K. Jernstedt, J. Org. Chem., 47, 4013
(1982).
80
A. Bogini, G. Cardillo, M. Orena, G. Ponzi, and S. Sandri, J. Org. Chem., 47, 4626 (1982).
81 J. J.-W. Duan and A. B. Smith, III, J. Org. Chem., 58, 3703 (1993).
82
M. Curini, F. Epifano, M. C. Marcotullio, and F. Montanari, Synlett, 368 (2004).