Asymmetric aldol reaction of thiazole-carbaldehydes: Regio- And stereoselective synthesis of tubuvalin analogues

The first organocatalytic enantioselective approach to precursors of tubuvaline (pre-Tuv) is presented employing a prolinamide-catalyzed aldol reaction of easily accessible thiazole-carbaldehyde with methyl isopropyl ketone "on water" in excellent yield as well as regio- and enantioselectivities. The analogues of pre-Tuv were achieved using an l-proline-catalyzed direct asymmetric aldol reaction of substituted thiazole-carbaldehydes with acetone. A direct and flexible approach to the tubavaline (Tuv) core of tubusylins has been established employing the reductive amination of the pre-Tuv species. The key aldol reaction should greatly expand the potential of this strategy to the synthesis of natural product tubulysins and a range of analogues.