Homologation of alkyl acetates, alkyl ethers, acetals, and ketals was accomplished
via formal insertion of diazo esters into carbon–carbon σ-bonds. The combined Lewis
acid InI3 with Me3SiBr catalyzed the homologation of alkyl acetates and alkyl ethers. That of acetals
and ketals was catalyzed solely by the use of InBr3. The key point of the homologation mechanism is that the indium-based Lewis acids
have the appropriate amount of Lewis acidity to achieve both the abstraction and release
of leaving groups. The abstraction of a leaving group by an indium-based Lewis acid
and the electrophilic addition of carbocation or oxonium intermediates to diazo esters
followed by the rearrangement of carbon substituents provide the corresponding cation
intermediates. Finally, the leaving group that is captured by the Lewis acid bonds
with cation intermediates to furnish the homologated products.
Key words
alkyl acetates - alkyl ethers - acetals - ketals - carbocations - diazo compound -
homologation - indium