REGIOSELECTIVITY IN [3+4]-ANNULATION AND [3+5]-ANNULATION REACTIONS OF BIS(TRIMETHYLSILYL) ENOL ETHERS WITH ACYLSILANE DICARBONYL DIELECTROPHILES

A number of 1,4- and 1,5-acylsilane dicarbonyl compounds were synthesized using Corey-Brook dithiane methods. These dicarbonyl substrates were annulated with the bis(trimethylsilyl) enol ether of methyl acetoacetate in the presence of TMSOTf, affording bicyclic ethers bearing silicon substituted at the bridgehead position: The annulation reactions proceeded with excellent regiochemical and good to excellent stereochemical control via a neighboring group participation mechanism. The silicon substituent was subsequently removed by treatment with fluoride ion. The overall transformation of annulation and desilylation represents a formal inversion of the regioselectivity normally exhibited with keto aldehyde dielectrophilic substrates in this process.