Formation of Cyclic Acetals from Allylic Hydroxy Phosphonates via Intramolecular Oxymercuration

Abstract

Treatment of allylic hydroxy phosphonates in aldehyde solution with mercuric trifluoroacetate, followed by the reduction of the organomercurial intermediate, afforded the cyclic acetal derivatives. The reaction displays high diastereo-and regio-selectivity. 31 P NMR studies showed the formation of an intermediate hemiacetal and rapid formation of the organomercurial upon addition of mercuric trifluoroacetate. However, the oxymercuration was reversible, and attempts to remove the excess aldehyde often led to recovery of the starting material. Fortunately, reduction of the organomercurial intermediate with sodium cyanoborohydride in the presence of the aldehyde led to more reproducible yields.

Trapping hemiacetals with phosphono substituted palladium π-allyl complexes for the synthesis of substituted cyclic ethers

“…4,5 Thus, treatment of a propanal solution of the hydroxy substituted phosphono allylic carbonate 8c with Pd(PPh 3 ) 4 gave the cyclic acetal 25 in 68% yield (Scheme 6). However, reaction of the same alcohol 8c with chloral hydrate in THF followed by treatment with Pd(PPh 3 ) 4 and Hunig's base resulted in the formation of formate 26 , presumably by elimination of chloroform from intermediate 27 , which was observed by 31P NMR spectroscopy.…”

“…5 A 31 P NMR spectrum of a solution of the hydroxy phosphonate in a mixture of propanal and CDCl 3 clearly showed the presence of equilibrium concentrations of hemiacetal. Further support is found in the report that allenyl aldehydes undergo palladium (II) catalyzed cyclization in alcohol solution under an atmosphere of CO to give THF-substituted unsaturated esters.…”