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Abstract
4-Substituted-4-triphenylphosphonro-5(4H)-oxazolones with a bulky alkyl substituent at the position 4 treated with MeOH in the presence of DBU (1.8-diazobicyclo[5.4.0]undec-7-ene) at room temperature give corresponding N-acyl-α-amino acid esters. In the case of a smaller substituent at the position 4 (Me, MeOCH2), the triphenylphosphonium group was competitively displaced by the methoxy group. The latter reaction can be avoided by carrying out hydro-de-phosphoniation in CH2Cl2 in the presence of only 150% excess of i-PrOH at 50°C in the absence of DBU. Possible mechanisms of hydro-de-phosphoniation are discussed.
