Substrate-Directed Diastereoselective Hydroformylation of Methallylic Alcohols

摘要

Structural units with two adjacent stereocenters are important targets in stereoseiective synthesis. In the construction of such units it is often advantageous to start with a compound already containing a stereocenter and to generate the secondstereocenter by substrate-directed asymmetric induction. For synthetic efficiency the second step should lead to an extension of the carbon framework. The hydroformylation of methallylic alcohols meets these requirements. However, preliminary studies with free methallylic alcohols showed, that in contrast to the rhodium-catalyzed hydrogenation of 2-substituted allylic alcohols, the hydroxyl functionality alone is not able to direct the reaction efficiently. Thus hydroformylation of the methallylic alcohol 1bgave a 1:1 synlanii mixture of the lactols 2. The diastereomer ratio was determined after oxidation to the lactones 3 (Scheme 1).