Mukaiyama 1 - -1 -cyclohexene

Several ketene silyl acetals add in a conjugate fashion to a,/3-unsaturated carbonyl compounds (Mukaiyama-Michael reaction) in the presence of LiC104. The more sterically demanding the ketene silyl acetals used, the greater is the concentration of LPDE required. For example, ketene silyl acetal Si-2 subjected to an LPDE solution (1.0 m) of 2-cyclohexen-l-one (12) gave 87 % of the 1,4 adduct whereas Si-3 required... 

The Mukaiyama aldol reaction of l-(trimethylsiloxy)-l-cyclohexene and benzalde-hyde has also been effected with the bidentate 188, giving the aldol products (erythro/ threo 1 3) in 87 % yield, though its monodentate counterpart 190 showed no evidence of reaction under similar conditions (Sch. 145). 

Scheme 8 shows the synthesis of 1 3-dialkylated cyclohexenes from 2-cyclohexenones consisting of 1 4-addition of organo-cupratesy enol phosphorylation and the final alkylation of the sp2 carbon. Scheme 9 provides a novel addition to the technique of 1 2-transposition of a carbonyl moiety accompanied by alkylation in tandem (15). The desulfurization is best performed by Mukaiyama s TiCl4 method (16). 

Bidentate Lewis acid. This useful catalyst (1) with a high propensity for double coordination of the carbonyl group is prepared from the corresponding phenol and two equivalents of McjAI in CH Clj at room temperature. It catalyzes the reduction of 5-nonanone by BujSnH at -78° in 86% yield, whereas a reaction in the presence of the monodentate 0-dimethylaluminum 2,6-xylenoxide affords 5-nonanol in only 6%.. Accordingly, different catalytic efficiencies are also found in the Mukaiyama aldol reaction (e.g., 87% vs. 0% in the reaction between 1-trimethylsiloxy-l-cyclohexene and benzaldehyde) and the Claisen rearrangement of (fil-cinnamyl vinyl ether (96% vs. 0%). The contrasting ( >Zi-selectivity of the Michael adducts also reflects the different coordination states. 

Maruoka and Ooi reported that a significant activation of carbonyl reactivity can be realized through the double coordination of carbonyl compounds by appropriate bidentate Lewis acids such as aluminum Lewis acid (17) prepared by treatment of the biphenylenediol (18) with Me3Al (2 equivalent) in CH2CI2 at room temperature for 30 minutes. The Mukaiyama aldol reaction of l-(trimethylsilyloxy)- -cyclohexene with benzaldehyde is effected by this bidentate Lewis acid (17) to give the aldol products in 87% yield (erythro/threo = 1 3). On the other hand, the use of its monodentate counterpart (19) did not produce the aldol products under similar conditions (Scheme 6.19). [26] Another examples of the carbonyl activation by bidentate aluminum Lewis acids are summarized in Section 6.6. 

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