Hindered amine stabilizers aldehyde

Surprisingly, such selectivity was observed only recently in an aldehyde series. Indeed the group of Barbas developed a catalyst able to perform anti-selective Michael addition of aldehydes [26]. To facilitate such a transformation, several parameters were adjusted to promote the formation of (Z)-enamine, which is necessary to obtain an anti-selectivity (i) the classical secondary amine catalyst was changed for primary amine 17, which is less sterically hindered, favoring the (Z)-enamine, and (ii) the substrate was chosen to be able to form a stabilizing intramolecular H-bonding in favor of the (Z)-enamine. For these reasons (tert-butyldimethylsilyloxy)acetaldehyde (18) was selected as pro-nucleophile. Excellent level of enantio- and diastereoselectivity were obtained on combining these both parameters (Scheme 34.1). In the postulated transition state, covalent interaction... 

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