Aza-Wittig Rearrangements of N‑Benzyl and N‑Allyl Glycine Methyl Esters. Discovery of a Surprising Cascade Aza-Wittig Rearrangement/Hydroboration Reaction
journal contributionposted on 18.09.2015, 00:00 by Renata K. Everett, John P. Wolfe
Treatment of N-(arylmethyl)-N-aryl or N-allyl-N-aryl glycine methyl ester derivatives with nBu2BOTf and iPr2NEt effects an aza-Wittig rearrangement that provides N-aryl phenylalanine methyl ester derivatives and N-aryl allylglycine methyl ester derivatives, respectively, in good yield with moderate to good diastereoselectivity. Under similar conditions, analogous substrates bearing N-carbonyl groups are converted to 1,4,2-oxazaborole derivatives. Additionally, N-allyl-N-aryl glycine methyl ester derivatives subjected to similar conditions at elevated temperatures undergo an aza-[2,3]-Wittig rearrangement, followed by a subsequent hydroboration oxidation reaction, to afford substituted amino alcohol products.