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

The lithio-derivative of methoxyallene reacts with aldehyde hydrazones leading 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 azetidines. The N-diallcylamino-3-methoxy-3-pyrrolines are transformed to 3-methoxy-3-pyrrolines by hydrogenolysis of the nitrogen-nitrogen bond, to 3-alkoxy-pyrroles by treatment with a peracid and to 3-amino-pyrroles by acidic migration of the dialkylamino group. In the case of SAMP-hydrazines, the obtained 3-methoxy-3-pyrrolines have a high enantiomeric purity. Lastly, attempts to prepare alpha -hydrazino-esters (and subsequently alpha -amino-esters) by ozonolysis of the allenyl moiety failed due to the formation of a methyl glyoxylate. (C) 2001 Elsevier Science Ltd. All rights reserved.