On the Mechanism of Cyclization of 5-Hexenylchromate Intermediates in the Reactions of Fischer Carbene Complexes with a Lithium Enolate and Allylmagnesium Bromide

Water freezing as a regiocontrol element in the multicomponent assembly of cyclic enones

Regioselective synthesis of dialkoxy 2-cyclopentenones and 2-cyclohexenones with novel substitution patterns has been accomplished by the one-pot combination of three simple starting materials (chromium carbene complex, Weinreb acetamide lithium enolate and 1-alkoxyallenyllithium) under either anhydrous conditions or water-promoted solidification of the reaction mixture. These results revealed an unprecedented water-freezing effect that plays a key role to completely reverse the regioselectivity of the intramolecular carbometalation of an allene moiety.