Mechanistic Insights into the Very Efficient [ReO_3OSiR_3]-Catalyzed Isomerization of Allyl Alcohols

摘要

The isomerization of allyl alcohols by the 1,3 transposition of an hydroxy group (Scheme 1 a) is catalyzed by certain high oxidation state transition metal oxo complexes, and has been carried out industrially by using [VO(OR)_3] or [WO(OR)_4] catalysts at high temperatures (ca. 130-200°C) for the production of terpenic alcohols. Recently Mo and V catalysts have been reported that are active at 25 °C. However, we find that in the case of the MoO_2X_2 complexes (X = Cl, OtBu), slow reduc--tion of theMo~(VI) center by the alcohol takes place, thereby causing a loss of catalytic activity with time, Based on these observations we have developed dioxomolybdenum(VI) catalysts that under appropriate conditions oxidize allyl and benzyl alcohols selectively to aldehydes.