Preparation of some angularly substituted and highly functionalized quinolizidines as building blocks for the synthesis of various alkaloids and related scaffolds of medicinal interest

The epimeric forms of the angularly substituted quinolizidine 6, representing potentially useful building blocks for the synthesis of various alkaloids, have been prepared via a pathway involving two consecutive ring-closing metathesis reactions. Variously hydroxy-protected derivatives (21, 22, and 26-29) of these compounds have also been generated.

The α-amino-α-vinylmalonate 10 is readily converted to piperidines 20 and 25, which when subjected (as a mixture of epimers) to RCM, affords the corresponding mixture of quinolizidines 21/22 and 26/27.