Rearrangements of Ylides Generated from Reactions of Diazo Compounds with Allyl Acetals and Thioketals by Catalytic Methods. Heteroatom Acceleration of the -Sigmatropic Rearrangement

Article abstract of DOI:10.1021/jo00185a014

Allyl acetals undergo ylide generation in rhodium(II) acetate catalyzed reactions with diazo esters with subsequent production of 2,5-dialkoxy-4-alkenoates by the <2,3>-sigmatropic rearrangement in moderate to good yields.The synthetic versatility of this class of polyfunctional compounds has been examined with selected transformations.Cyclopropanation and Stevens rearrangement compete with the <2,3>-sigmatropic rearrangement in certain cases, and the influence of reactant structure and reaction conditions on this competition is reported.Comparative results with allyl ethers, which undergo cyclopropanation almost exclusively, demonstrate that heteroatom substitution on the allylic carbon accelerates ylide rearrangement.With dithioketals such as 2-ethenyl-2-methyl-1,3-dithiane, the ylide generated from Rh2(OAc)4 catalyzed reactions of ethyl diazoacetate undergoes <2,3>-sigmatropic rearrangement in competition with intramolecular eliminination but without evidence of either cyclopropanation or Stevens rearrangement.Only when the <2,3>-sigmatropic rearrangement cannot occur competitively does the Stevens rearrangement become important in reactions with dithioketals.In these examples the catalytic methodology for ylide generation is advanced as an attractive alternative to base promoted methodologies.