Diastereoselective Reduction of Alkenes

Diastereoselective hydrogenations of this type have been reported by Burgess and coworkers [54—59] using chiral-protected and -unprotected allylic and homo allylic alcohols as substrates with their carbene catalyst lr(9). Catalyst control was found to be dominant, but depending on the position and nature of the oxygen substituents, moderate to strong match/ mismatch effects were observed. 

A reasonably large difference in diastereomeric excess was observed between product 47b with an adjacent methyl ester and 48b with a primary alcohol in the equivalent position [57]. It was noted by the authors that in cases involving a 1,3 system, changing the pendant group from a primary allylic alcohol to a methyl ester caused a reversal of facial selectivity [54, 58]. The same effect was absent in the 1,2 systems 51b and 52b studied. The diastereomeric ratio in the latter case was attributed mainly to catalyst control [58]. 

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