Gallium(III) Triflate Catalyzed Conversion of Aldehydes and Ketones to Hydantoins

Abstract

Reported is the one-pot synthesis of hydantoins from aldehydes and ketones using gallium-catalyzed cyanoamination. Reported also is a two-pot process which showed a significant advance upon the traditional Bucherer-Bergs reaction, but suffered from problems of isolation and purification of the intermediate amino nitriles. In order to circumvent these problems, a one-pot procedure was developed. This procedure consists of addition of liquid ammonia at -78 °C to an aldehyde or ketone and gallium(III) triflate, followed by addition of HCN. Allowing the reaction mixture to warm to room temperature (evaporation of NH3) followed by addition of Hünigs base and gaseous CO2 delivered the desired hydantoins in reasonable to excellent yields. The two- and one-pot reactions were compared and the one-pot reaction gave similar or better yields. Significantly, benzaldehyde, 2-aceto­naphthalene and nonan-5-one, gave very poor (0-3%) combined yields in the two-pot reaction due to problems of isolation and purification of the amino nitriles, but good yields in the one-pot reaction.