Reaction of β-formylporphyrins with organometallic reagents -: A facile method for the preparation of porphyrins with exocyclic double bonds

5,10,15,20-Tetralkyl-2-formylporphyrins were treated with various organolithium reagents to form porphyrins with exocyclic double bonds. The reaction involved conversion with LiR to the respective alcohol. Subsequence dehydratization of the alcohols yielded olefinic systems in which the double bond formed was located in the meso substituent neighboring the beta position, i.e., the result of a 1,5-hydride shift. Depending on the organolithium reagent used various olefinic porphyrins are accessible, provided the stability of the intermediary carbenium ion is high enough. Furthermore, use of a Peterson olefination allowed the facile synthesis of 2-vinyl-5,10,15,20-tetralkylporphyrins and use of an organodilithium reagent gave convenient access to functionalized bisporphyrins. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.