Selective reductions of substituted hydantoins

Nine N-3-substituted hydantoins (2) have been shown to undergo LiAlH4 reduction (tetrahydrofuran, room temperature, 2d) to give 4-hydroxy-2-imidazolidinones (21) in good yields. Reduction of 3,5-disubstituted hydantoins in which an aliphatic substituent was present at nitrogen-3 led to the preferential formation of the cis-adduct 21. Conversely, disubstituted hydantoins possessing an aryl moiety at nitrogen-3 gave the trans-derivative 21 as the major product. Treatment of the N-3- Substituted hydantoins (2) under more vigorous conditions (tetrahydrofuran, reflux, 3d) led to selective ring opening of 2 to yield N-methylethylenediamine derivatives (1). The scope of both of these reductive processes has been explored and explanations offered to account for the observed results. The reactivity of the 4-hydroxy adducts (21,) was examined. Treatment of 21 with trifluoroacetic acid gave the corresponding 2-imidazolones (18). Conversely, reaction of suitably N-3-sub- Stituted derivatives (21) with trifluoroacetic acid and trifluoroacetic anhydride in methylene chloride led to the annelated adducts 39^. The latter reaction required the presence of two substituents at carbon-5. [...]