REARRANGEMENTS OF NONRACEMIC VINYL PHOSPHATES TO BETA-KETO PHOSPHONATES

A series of chiral auxiliaries has been tested for viability in the vinyl phosphate/beta-keto phosphonate rearrangement. While dienyl phosphates derived from ephedrine, pseudoephedrine, and isopinocampheol succumbed to competing elimination reactions, ones derived from menthol and (S)-2-methylbutanol were found to undergo rearrangement to the desired beta-keto phosphonates. The bis((S)2-methylbultyl) phosphorochloridate then was used to prepare the vinyl phosphates of the prochiral ketone 4-methylcyclohexanone, and modest diastereoselectivity was observed upon rearrangement of these phosphates to the corresponding beta-keto phosphonates. The de of this rearrangement was established by degradation of the beta-keto phosphonate to 3-methyladipic acid and determination of the optical rotation. This sequence allowed identification of the major rearrangement product as the 4R-diastereomer of beta-keto phosphonate 13. Finally, two other prochiral cyclohexanones were found to be suitable substrates for the vinyl phosphate/beta-keto phosphonate rearrangement.