Diarylprolinols trimethylsilyl ether

Scheme 2.15 Domino Michael-crossed benzoin reaction catalysed by a combination of a chiral diarylprolinol trimethylsilyl ether and a triazolium salt.

A remarkable multicatalytic relay system consisting of tetra-propylammonium perruthenate/N-methylmorpholine iV-oxide (TPAP/NMO) as oxidant, and chiral diarylprolinol trimethylsilyl ethers as organocatalysts, has recently been developed by Rueping et al. and applied in the efficient construction of various valuable chiral molecules through domino reactions. The latter were all based on the in situ generation of ot,p-unsaturated... 

Scheme 2.5 Conformations and shielding effect of diarylprolinol trimethylsilyl ether-derived...

The initial experimental report due to Enders and coworkers demonstrated that diarylprolinol trimethylsilyl ether can generate four contiguous stereocenters with a high degree of stereoselectivity in favor of (3S,4S,5R,6R)-2-methyl-5-nitro-4,6-diphenylcyclohex-l-ene carbaldehyde as the final product [46]. More importantly, mechanistic investigations aimed to establish the reasons behind the isolation of only two epimers out of 16 possible stereoisomers. 

In contrast to the use of the specific type of sulfur ylides and related compounds, the employment of readily available alkyl halides for a catalytic Michael-alkylation reaction with enals to produce the corresponding formal [2-1-1] cycloadducts is an extremely challenging task. As an example, Wang [82a] and Cordova [82b, 83a] independently reported the enantioselective organocatalytic reaction of bromoma-lonates 78 and enals, which led to the corresponding cyclopropanes 79. In both cases, chiral diarylprolinol trimethylsilyl ethers 8 and 80 were involved as catalysts, giving access to the corresponding 2-formylcyclopropane derivatives 79 in... 

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