Reaction of the lithio-derivative of methoxyallene with hydrazones. Part 1: Synthesis and transformation of alpha-allenyl hydrazines

The lithio-derivative of methoxyallene reacts with aldehyde hydrazones lead ing to expected alpha -allenyl hydrazines when ether is the solvent of the reaction. The yields are good as well as the diastereoselectivity observed in the case of SAMP-hydrazones. These hydrazines are cleanly transformed to N-dialkylamino-3-methoxy-3-pyrrolines when they are reacted with n-BuLi in THF. These compounds are sometimes accompanied by the isomeric 4-methyl az etidines. The N-diallcylamino-3-methoxy-3-pyrrolines are transformed to 3-m ethoxy-3-pyrrolines by hydrogenolysis of the nitrogen-nitrogen bond, to 3-a lkoxy-pyrroles by treatment with a peracid and to 3-amino-pyrroles by acidi c migration of the dialkylamino group. In the case of SAMP-hydrazines, the obtained 3-methoxy-3-pyrrolines have a high enantiomeric purity. Lastly, at tempts to prepare alpha -hydrazino-esters (and subsequently alpha -amino-es ters) by ozonolysis of the allenyl moiety failed due to the formation of a methyl glyoxylate. (C) 2001 Elsevier Science Ltd. All rights reserved.