Meyer-Schuster rearrangement mechanism

Andres, J., Silla, E., Tapia, O. A quantum chemical study of protonated intermediates in Rupe and Meyer-Schuster rearrangement mechanisms. THEOCHEM 1983,14, 307-314. 

The iron(III) chloride-catalyzed ring expansion reaction of 2-azetidinone-tethered alkynols and allenols provides pyrroles or y-lactones, respectively (Scheme 4-351). The proposed mechanism for the pyrrole formation includes a Meyer-Schuster rearrangement of the propargyl alcohol to the corresponding allenyl alcohol, P-lactam ring opening, tautomerization of the allenyl alcohol to the a,P-unsaturated carbonyl compound, and cyclization by attack of the amino group to the ketone under dehydration. ... 

DFT study of interception of the allenyl enolate intermediate of Meyer-Schuster rearrangement using aldehydes and imines has shown that the active form of the vanadium catalyst bears two triphenyl siloxy ligands and that vanadium enolate is directly involved in the C-C bond formation." DFT calculations have elucidated the mechanisms and diastereoselectivities of phosphine-catalysed [4-1-2] annulations between allenoates and ketones or aldimines (Scheme 44). 

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