NEW SYNTHESES OF METHYLENIMINIUM SALTS FR OM CARBONYL-COMPOUNDS AND FROM ALPHA-CHLORO ETHERS - AN ACCESS TO VINYLOGOUS VIEHE SALTS

Two methods for the synthesis of isolable methyleniminium salts and am idinium salts are presented. In the first case carbonyl compounds A ar e treated with a mixture of (dialkylamino)trimethylsilane (12) and chl orotrimethylsilane (13) or 12 and trimethylsilyl triflate (14) leading to the iminium chlorides F or iminium triflates G, respectively. With 12/13 the preparation of F is limited to non-enolizable aldehydes and dimethylformamide (10), while 12/14 enables the preparation of G, e.g . 23a-25a, 27a, also with ketones and with substituted amides. The sec ond procedure is based on the treatment of alpha-chloro ethers L with 12. Both methods afford the Mannich reagent 16a in high yields. By rea ction of the alpha-chloro ether 35 with 12 in diethyl ether the vinylo gous Viehe salts 36a-c, e become available for the first time. The rea ction pathways are discussed.