Experimental Test of Setting Three Contiguous Stereogenic Centers in Water. Diastereoselective Coupling of Geometrically Biased Allylic Bromides to α-Oxy Aldehydes with Indium

Indium-promoted additions of ( Z )-2-(bromomethyl)-2-butenoate to several α-( tert -butyldimethylsiloxy) and α-(benzyloxy) aldehydes in water have been examined in order to assess the direction and sense of asymmetric induction in these coupling reactions. High levels of the 3,4-syn;4,5-anti diastereomers were produced, reflecting the promising synthetic potential of this chemistry. This stereodifferentiation has been attributed to the strong geometric bias exercised by this allylindium reagent and adherence to a Felkin−Ahn transition-state alignment. Support for this interpretation was gained by comparing the fate of ( E )-cinnamyl bromide under comparable circumstances. In this case, the 3,4-anti;4,5-anti diastereomer predominated as expected.