Organomolybdän‐ und Organowolfram‐;Reagenzien, IV. über die Chemoselektivität des carbonylmethylenierenden Reagenzes aus 2 MoOCl 3 (THF) 2 und 4 CH 3 Li

Organomolybdenum and Organotungsten Reagents, IV. — About the Chemoselectivity of the Carbonylmethylenating Reagent from 2 MoOCl 3 (THF) 2 and 4 CH 3 Li From a series of carbonylolefinating Mo complexes the reagent “3”, obtained by low‐temperature methylation of two equivalents of MoOCl 3 (THF) 2 with four equivalents of methyllithium and warming up, is especially favourable for chemoselective carbonylolefination reactions. It is readily accessible, reacts at low temperatures, exhibits high aldehydeversus‐ketone selectivity (Tables 1, 2; Scheme 2), high cheleselectivity (preference of a keto group in the α‐ or β‐ position to a hydroxy group before an isolated keto group: Table 4; Scheme 3), and in some cases anticheleselectivity (Table 6). It is nonbasic and tolerates hydroxy groups (even water in the solvent) as well as acyl chloride groups (Table 8). — The chemoselectivity of 3 is compared in several cases with other carbonylolefinating reagents.