Titanium catalysts asymmetric principles

The fundamental principles of asymmetric synthesis employed throughout also apply to ene reactions. Chiral additives, chiral auxiliaries, and the preparation of chirons all lead to good enantioselectivity when applied to the ene reactions. Most chiral ene reactions seem to involve addition of a chiral catalyst or the use of a chiral auxiliary. Oppolzer et al. utilized a chiral auxiliary in 713 to prepare 714 (90 % de) in a synthesis of (+)-a-allokainic acid.515 Yamamoto used the chiral aluminum catalyst 715 for the intermolecular ene reaction of 1,6-dichlorobenzaldehyde and 2-phenylthio-l-propene to give 716 in 96% yield (65 % ee).5i6 These catalysts are similar to those used in Section 11.9.B. A similar titanium catalyst (717) was used to couple methylenecyclohexane and methyl glyoxalate, giving 89% of 718 (98 % ee). The titanium catalyst... 

Asymmetric catalytic addition of dialkylphosphites to a C=0 double bond is a powerful method, and probably the most general and widely applied, for formation of optically active a-hydroxy phosphonates [258], The basic principle of this reaction is shown in Scheme 6.108. Several types of catalyst have been found to be useful. The transition-metal-catalyzed asymmetric hydrophosphonylation using chiral titanium or lanthanoid complexes was developed by several groups [259, 260], The most efficient type of chiral catalyst so far is a heterobimetallic complex consisting... 

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