A straightforward synthesis of didehydro analogues of N-acetylardeemin

The didehydro analogue of N-acetylardeemin 1b was synthesised in a seven st ep process that started with tryptamine. A regioselective oxidation of the 2-substituted precursor 3b, followed by a diastereoselective anti-cyclizati on reaction involving an acyliminium intermediate formed from the unisolate d tosylate 2b, is the key-step of this strategy. Application of this proced ure to 3a afforded, instead of the cyclization product, the cis-1-hydroxy d erivative 2c which, after acid treatment, gave a 6/4 mixture of trans- and cis-isomers of the hexacyclic compound 1a. (C) 2000 Elsevier Science Ltd. A ll rights reserved.