Page 898 - Advanced Organic Chemistry Part B - Reactions & Synthesis

874 The stereoselectivity of the (CH AlCl-catalyzed reaction has also been found to be
3 2
sensitive to the steric bulk of the aldehyde. 34
CHAPTER 10 The use of Lewis acid catalysts greatly expands the synthetic utility of the
Reactions Involving carbonyl-ene reaction. Aromatic aldehydes and acrolein undergo the ene reaction with
Carbocations, Carbenes, 35
and Radicals as Reactive activated alkenes such as enol ethers in the presence of Yb(fod) . Sc(O SCF has
3
3
3 3
Intermediates also been used to catalyze carbonyl-ene reactions. 36
Sc(O SCF )
3
3 3
ArCH O + CH 2 Ar
Ac 2 O, CH CN O 2 CCH 3
3
Among the more effective conditions for reaction of formaldehyde with -
methylstyrenes is BF in combination with 4A molecular sieves. 37
3
CH 3 BF 3 CH 2
+ (CH 2 O) n 4 A M.S. Ar OH
Ar CH 2

The function of the molecular sieves in this case is believed to be as a base that
sequesters the protons, which otherwise would promote a variety of side reactions.
With chiral catalysts, the carbonyl ene reaction becomes enantioselective. Among the
successful catalysts are diisopropoxyTi(IV)BINOL and copper-BOX complexes.

+ O CHCO C H t Bu-BOX CO C H
2 2 5
2 2 5
Cu(O SCF ) H OH
3 2
3
96% e.e.
Ref. 38
R-BINOL-TiCl 2 OH
+ CF CH O
CH 3 3 4 A M.S.
CF 3
CH 3
94% yield, 98% syn, 96% e.e.
Ref. 39

CH 3 OH
Ti/BINOL
(i-PrO) 2
(CH 3 ) 2 C CH 2 + O CHCO 2 CH 3
CH 2 CO CH 3
2
72% yield, 95% e.e.
Ref. 40
34 T. A. Houston, Y. Tanaka, and M. Koreeda, J. Org. Chem., 58, 4287 (1993).
35
M. A. Ciufolini, M. V. Deaton, S. R. Zhu, and M. Y. Chen, Tetrahedron, 53, 16299 (1997);
M. A. Ciufolini and S. Zhu, J. Org. Chem., 63, 1668 (1998).
36 V. K. Aggarawal, G. P. Vennall, P. N. Davey, and C. Newman, Tetrahedron Lett., 39, 1997 (1998).
37 T. Okachi, K. Fujimoto, and M. Onaka, Org. Lett., 4, 1667 (2002).
38
D. A. Evans, C. S. Burgey, N. A. Paras, T. Vojkovsky, and S. W. Tregay, J. Am. Chem. Soc., 120,
5824 (1998).
39 K. Mikami, T. Yajima, T. Takasaki, S. Matsukawa, M. Terada, T. Uchimaru, and M. Maruta, Tetra-
hedron, 52, 85 (1996).
40
K. Mikami, M. Terada, and T. Nakai, J. Am. Chem. Soc., 112, 3949 (1990).