Photocyclisation of enamides .39. General strategy for the synthesis of pseudodistomins: Synthesis of triacetates of (+/-)-tetrahydropseudodistomin and proposed structures of pseudodistomins A and B

A synthetic strategy of pseudodistomin was developed by first synthesizing the (+/-)-(2 alpha,4 beta,5 beta)-5-amino-2(3-hydroxypropyl)piperidin-4-ol 14 as a key intermediate via a route involving the reductive photocyclisation of enamide 5 followed by the introduction of a three-carbon side-chain by application of an a-acylamino photo-induced radical allylation by allyltributyltin replacing a methylsulfanyl group, The key intermediate 14 was then converted into the piperidines 19 and 20, with a dienyl side-chain, which have the structures proposed for pseudodistomins A 1 and B 2. However, direct comparisons with the triacetates of the natural alkaloids have shown that a revision of the proposed structures is required.