Lactam synthesis oxygen nucleophiles

M-Acyliminium cyclizations of optically active mono- and di-oxygenated hydroxylactam derivatives have been used in the synthesis of a number of natural products. In case of a five-membered lactam the oxygen function adjacent to the iminium carbon directs attack of the internal nucleophile from the least hindered side, opposite to the substituent. In the examples given the size of the newly formed ring is determined by the electronic bias of the alkene substituent. 

Enantiopure a, ft -unsaturated 5-lactams react stereoselectively with carbon-, nitrogen-, sulfur-, and oxygen-centred nucleophiles [N3-, Me(CH2)nS, MeO-, and n-Bu-]. The synthetic potential of these conjugate additions has been demonstrated through the synthesis of two new substituted indolizidines, (7/f)-7-amino-8-deoxy-swainsonine and (7/ )-7-acetylaminoswainsonin.133... 

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