Spiro-Fused 2,5-Cyclohexadienones from the Thermal 1,3-Alkyl Migrations of Quinol Vinyl Ethers. A Strategy for Conversion of a Carbonyl Carbon to a Quaternary Carbon

Article abstract of DOI:10.1021/jo00283a035

Reaction of p-benzoquinone monoketals with 2-lithio derivatives of acetophenone and propiophenone dimethyl ketals results in organolithium addition to the carbonyl group of the quinone monoketal to afford the ketals of 4-aryl-4-hydroxy-1,5-cyclohexadienones.Reaction of these products with aqueous acid results in hydrolysis of 2,5-cyclohexadienone ketal and intramolecular mixed ketal formation between 4-hydroxyl group and the 2-substituted acetyl or propionyl side chain of the aromatic ring.Conversion of this cyclic ketal to the vinyl ether by loss of methanol affords the quinol ether derivatives for thermolysis.Variants of this chemistry were used to prepare a number of spiro-fused vinyl ethers of the p-quinols.At 130-170 deg C these molecules undergo high-yield conversion of the vinyl ether moiety to a ketone, affording spiro-fused 4,4-disubstituted 2,5-cyclohexadienones.Rates have been measured for several of these formal <1,3>-shifts, and a ρ value of -0.87 was calculated for rearrangement of compounds having aryl substituents on the vinyl ether double bond.This chemistry establishes a high-yield strategy for conversion of p-benzoquinone monoketals, 4,4-dialkoxy-2,5-cyclohexadienones, to spiro-fused 2,5-cyclohexadienones.