Cinchona stereoselectivity, origin

Figure 4.2 Origin of stereoselectivity of cinchona-derived quaternary ammonium salts.

The hybrid thiourea-cinchona alkaloid catalyst 14 proved to be effective in a stereoselective Michael addition reaction between a,p-unsaturated y-butyrolactam 11 and chalcone 12 (Scheme 3.22). The following mechanistic study addressed the issue of the origin of sfereoselecfion. 

A double-Michael addition of benzofuran-2-ones to divinyl ketones (RCH=CH)2CO, catalysed by various cinchona alkaloid-derived thioureas, has been shown to form spiro-cyclic benzofuran-2-ones (291) with <92% ee and <10 1 dr. DFT calculations were used to shed light on the origin of the stereoselectivity. ... 

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