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

Significance

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.