Allylation aldehydes with allylsilane catalyzed

Scheme 13.10 Allylation aldehydes with allylsilane catalyzed by Yb Lewis acid.

The CAB-catalyzed reactions of aldehydes with allyl- and crotylsilanes are summarized in Table 11-28 [288, 309], These data show that the CAB-catalyzed crotylation reactions with crotylsilanes 123b and 460 are highly diastereo- and en-antioselective, while the corresponding allylation reactions with allylsilanes 131 occur with somewhat lower enantioselectivity. 

Si. rra(pentafluorophenyl)boron was found to be an efficient, air-stable, and water-tolerant Lewis-acid catalyst for the allylation reaction of allylsilanes with aldehydes.167 Sc(OTf)3-catalyzed allylations of hydrates of a-keto aldehydes, glyoxylates and activated aromatic aldehydes with allyltrimethylsilane in H2O-CH3CN were examined. a-Keto and a-ester homoallylic alcohols and aromatic homoallylic alcohols were obtained in good to excellent yields.168 Allylation reactions of carbonyl compounds such as aldehydes and reactive ketones using allyltrimethoxysilane in aqueous media proceeded smoothly in the presence of 5 mol% of a CdF2-terpyridine complex (Eq. 8.71).169... 

Catalytic asymmetric allylation of aldehydes and ketones with allylsilanes can be achieved by using chiral Lewis acids, transition metal complexes, and Lewis bases. In recent years, much attention has been paid for the chiral Lewis base-catalyzed system using allyltrichlorosilanes. Advances in catalytic asymmetric carbonyl allylation have been described in detail in recent reviews.116,117,117a... 

Allylations. P-Hydroxylamino aldehydes undergo TiCl -catalyzed allylation with allylsilanes to provide 5-allylisoxazolidines. This approach offers an alternative to direct... 

Addition to C=0. Hydrates of a-ketoaldehydes react selectively at the aldehyde group with allylsilanes under the influence of YbfOTfjj at room temperature. The allylation of aldehydes with allylstannanes is accelerated by benzoic acid." Another method for the synthesis of homoallylic alcohols is by the ene reaction, thus y,6-unsaturated a-hydroxy esters are obtained from glyoxylic esters at room temperature in a catalyzed process. ... 

Allylation adducts of ( )-Y-(dimethylphenylsilyl)allylboronate 47 selectively undergo addition reactions with aldehydes. Lewis acid catalyzed [3 + 2] cycloaddition reaction of these allylsilanes with various aldehydes, e.g., 55, provides tetrahydrofuran adducts with high diastereoselectivity. ... 

Homoallylk ethers. lodotrimethylsilane catalyzes the allylation of acetals and ketals by allylsilanes, with transposition of the allylic group (equation I). It does not catalyze allylation of aldehydes and ketones. Note that TiCI can catalyze both of these reactions (7, 370-371). In this respect, ISi(CH3)3 resembles (CH3)3SiOTf (this volume). 

A chiral reagent derived from tin(II) catecholate, DBU, allyl bromide, and (+)-di-/-butyl tartrate reacts with aromatic aldehydes in a Cul-catalyzed reaction, giving homoallylic alcohols sometimes in excellent optical purities. Allylation with allyltrichlorosilane has been conducted in the presence of 45 and 46 (cf. allenylation of aliphatic aldehydes ). Allylsilanes modified by a tartrate ester show a range of effectiveness in chirality transfer. ... 

In the last decade there have been remarkable advances in the syntheses and applications of optically active a-chiral allylsilanes. Asymmetric hydrosilylation of 1,3-dienes provides convenient access to these allylsilanes [387]. Hayashi et al. have demonstrated tliat axially chiral monophosphines (MOP) are efficient chiral ligands in the Pd-catalyzed asymmetric hydrosilylation [388]. In particular, the MOP ligand 124 can realize high catalytic activity and enantioselectivity in the reaction of cyclic 1,3-dienes with HSiCL (Scheme 10.137) [388a,b]. The allyltrichlorosilanes obtained are quite valuable for highly diastereo- and enantioselective allylation of aldehydes by Kobayashi s procedure [371]. 

Acyloxyborane catalyzed allylation (cf. 16,314). The acyloxyboranc 1, obtained by reaction of borane THF with (2R,3R)-2,6-diisopropoxybenzoyltartaric acid, catalyzes the reaction of allylsilanes with aldehydes to afford. vyn-homoallylic alcohols with >80% cc. The geometry of the silane has no effect on the. syn-selcctivity. 

Miscellaneous Reactions. AICI3 has been used to catalyze the addition of allylsilanes to aldehydes and acid chlorides (eq 37). Cyclic ethers (pyrans and oxepins) have been prepared with hy-droxyalkenes (eq 38). The course of reactions between aldehydes and allylic Grignard reagents can be completely diverted to a-allylation by AICI3 (eq 39). The normal course of the reaction gives y-allylation products. 

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