Tricyclic silyl aldolate

Treatment of ketone (69) with excess amounts of t-BuMe2SiOTf and bis[(k)-l-phenylethyl]amine ((i )-BPEA) gives tricyclic silyl aldolate (70) with moderate enantioselectivity [104]. The formation of (70) can be explained by the enol silylation to (71) followed by a tandem Michael-aldol reaction. The asymmetric induction by the chiral amine occurs in the enol silylation (Scheme 9.40). The combined use of silyl triflates and amines has been applied to an intramolecular aldol reaction for natural product synthesis [105]. 

In 2009, a diarylprolinol silyl ether was involved as an organocatalyst in an asymmetric domino aldol-oxa-Michael reaction occurring between salicy-laldehyde and senecialdehyde. As shown in Scheme 2.28, this process generated the corresponding chiral tricyclic systems in good yields and high enantioselectivities of up to 98% ee. One of these products could be further converted into 4-dehydroxydiversonol. 

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