The first enantioselective organocatalytic alpha-nitroatkylation of aldehydes has been accomplished. The aforementioned process involves the oxidative coupling of an enamine intermediate, generated transiently via condensation of an amine catalyst with an aldehyde, with a silyl. nitronate to produce a beta-nitroaldehyde. Two methods, one that furnishes the syn beta-nitroaldehyde and a second that provides access to the anti isomer, have been developed. Data are presented to support a hypothesis that explains this phenomenon in terms of a silyl group-controlled change in mechanism. Finally, a three-step procedure for the synthesis of both syn- and anti-alpha,beta-disubstituted beta-amino acids is presented.