| Abstract: | A Simple Synthesis of Alkyl Allenecarboxylates (Allenic Esters) by the Wittig-Reaction A simple one-pot synthesis of variously substituted α-allenic esters ( 7–23 , cf. Scheme 4) is described. Either of the phosphonium salts 1 and 2 or the phosphoranes 3–6 in methylene chloride (or acetonitrile) when treated with acid chlorides at room temperature in the presence of triethylamine give the corresponding allenic compounds in fairly good yields (cf. Tables 3a and 3b). This procedure shows for the first time, that the Wittig-reaction with acid chlorides as starting material can also be used for the synthesis of 2-H-substituted allenic esters ( 7–13 ; for numbering see Scheme 7). The deuterium labeled compounds 26–31 (cf. Scheme 7) are prepared in the same manner. The course of the reaction involves an in situ generation of ketenes which are trapped by the resonance stabilized phosphonium ylides. The thus formed betains readily decompose, already at room temperature, to the anticipated allenes by the well known Wittig-reaction. |
