Aldehydes allyl trichlorosilane

S)-Prolinc-dcrivcd phosphoramides catalyse enantioselective allylation of aromatic aldehydes with allylic trichlorosilanes.90 Chiral a-aminoaldehydes have been allylated diastereoselectively with various reagents.91... 

Stereo specific generation and reactions of allylic alkali and alkaline earth metals have been reviewed121 and solvent-mediated allylation of carbonyl compounds with allylstannanes has been explored.122 Chiral phosphoramides derived from (5 )-proliiie have been used to catalyse asymmetric allylation of aromatic aldehydes by allylic trichlorosilanes.123... 

Chiral phosphoramides have been developed as catalysts for asymmetric addition of allylic trichlorosilanes to aldehydes.176 Although some des were high, ees were modest. Kinetic studies suggest dual mechanisms, and thus a route to the design of more highly selective catalysts. 

Scheme 7.2 Lewis base-catalyzed allylation of aldehydes 1 with allyl trichlorosilanes 2a-d.

Allyl trichlorosilane (0.47 mmol) was added to a solution of the METHOX catalyst (0.02 mmol), diisopropylethylamine (2 mmol) and aldehyde (0.4 mmol) in acetonitrile (2 mL) under nitrogen at — 40 °C. The mixture was stirred at the same temperature for 18 h, after which the reaction was quenched with aqueous saturated NaHC03 (1 mL). The aqueous layer was extracted with ethyl acetate (3 x 10 mL) and the combined organic extracts were washed with brine and dried over Na2S04. The solvent was removed in vacuo and the residue purified by FC on a silica gel column (15 cm x 1 cm) with a petroleum ether-ethyl acetate mixture (95 5) to produce (S)-(—)-l-phenyl-but-3-en-l-ol (95%, 96% ee). 

Pentacoordinate silicon, in the form of allyltrichlorosilane, in the presence of DMF or HMPA, also undergoes allylation with aldehyde [97,98], The Lewis base-promoted approach has the merit of operational convenience. Stereoselective formation of allylic trichlorosilanes is achieved by copper-catalyzed coupling of allylic chloride and trichlorosilane or by palladium-catalyzed hydrosilylation of 1,3-dienes (Sch. 56) [99],... 

Chiral phosphorarnides, as developed by Denmark during the late 1990s [25], are efficient catalysts for the allylation of aldehydes with allyl trichlorosilane [26a] or the aldol condensation of trichlorosilyl-enol ethers with aldehydes [26b]. However, the first example of supported chiral phosphorarnides on a polymeric matrix was reported only in 2005 [27]. 

Stoichiometric asymmetric allylation of (V-benzoyl hydrazones derived from aromatic and heteroaromatic aldehydes can be attained with pseudoephedrine chelates derived from allyl and ( )- and (Z)-crotyl trichlorosilanes with excellent diastereo- and enantioselectivity (eq 7) note the opposite relative configuration at the vicinal centers of the product compared to that obtained in the aldehyde allylation (eq 4), resulting from different orientation in the transition state. ... 

Denmark SE, Fu J, Coe DM, Su X, Pratt NE, Giiedel BD (2006) Chiral phosphoramide-catalyzed enantioselective addition of allylic trichlorosilanes to aldehydes, preparative and mechanistic studies with monodentate phosphoms-based amides. J Org Chtan 71 1513-1522... 

Chiral Lewis-basic catalysts (Figs. 7.1 and 7.2), in particular phosphoramides 8-12 [9, 14c, 15c, 22-24], formamide 13 [17], pyridine N,N -bisoxides 17 and 18 [25-27], N-monoxides (19-26) [27-32], and N,N N"-trisoxides (27) [33] exhibit good to high enantioselectivities for the allylation of aromatic, heteroaromatic, and cinnamyl-type aldehydes (1) with allyl, trans- and ds-crotyl, and prenyl trichlorosilanes (2a-d). Chiral formamides (with the exception of 13, as discussed below) [17], pyridine-oxazolines [34], urea derivatives [19] and sulfoxides [35] are effective only in stoichiometric quantities (or in excess) and, as a rule, exhibit lower enantioselectivities. 

The addition of allyltributylstannane to aldehydes can also be effected with equimolar amounts of MeSiCl3 or MeSiCl(OMe)2 (Eq. 13) [21]. The initial product is the silyl ether which is hydrolyzed in the aqueous work-up. An allylic silane intermediate was shown not to be involved in the addition. The reaction with benzaldehyde could be accomplished with 0.33 equiv. of trichlorosilane but at a much slower rate. The product of this addition was cleaved by treatment with KF or aqueous acetic acid in THE... 

Reactions of propargyl trichlorosilane (21.90) with aromatic, heteroaromatic, and cinnamyl-type aldehydes (21.4), promoted by DMF, have been shown to occur in analogy to the allylation, producing allenyl alcohols 21.91 with >99 1 selectivity (Scheme 21.12). Similarly, allenyl trichlorosilane (21.92)... 

Chiral Lewis-basic catalysts, in particular phosphoratnides (1 and 2),2-13c. 16.46,47 pyridine iV,iV-bisoxides (3 and and pyridine iV-monoxides (5, 6 and 7,8),3 exhibit very high enantioselectivities for the allylation of aromatic, heteroaromatic, and cinnamyl-type aldehydes with allyl, ( )- and (Z)-crotyl, and prenyl trichlorosilanes. Chiral formamides, pyridine-oxazolines, urea derivatives, and sulfoxides are generally less enantioselective and effective only in stoichiometric quantities. The reaction is much less efficient with aliphatic aldehydes, which require stoichiometric conditions (vide infra). However, a, -unsaturated aldehydes do react readily and give 1,2-addition products. 

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