Synthesis of Novel Quaternary Amino Acids Using Molybdenum-Catalyzed Asymmetric Allylic Alkylation

The Mo-catalyzed asymmetric allylic alkylation using azlactones provides extraordinary levels of selectivity. Thus, a wide range of cinnamyl-type substrates react with 2-methyl and 2-benzyl azlactones to give only the product resulting from attack at the more substituted carbon. Using other alkyl substituents such as 2-methylthioethyl, isobutyl, allyl, and isopropyl provides products that still retain excellent regioselectivity but small quantities of the linear product are also observed. In all cases, excellent diastereo- and enantioselectivity of the branched alkylated product are observed. This new asymmetric reaction provides ready access to unusual quarternary amino acids, important building blocks for biological applications. The reactions complements the Pd AAA wherein the cinnamyl substrate leads to only the product of attack at the primary terminus of the allyl moiety.