Novel LiAlH4 Reduction Pathway. Reactions of 2,3-Dihydro-1H-imidazopyrazol-2-ones with LiAlH4. Preparations of 2,3-Dihydro-1H-imidazopyrazoles and Side Products

Article abstract of DOI:10.1021/jo00199a020

The direct LiAlH4 reduction of 2,3-dihydro-1H-imidazo<1,2-b>pyrazol-2-ones, 2, to 2,3-dihydro-1H-imidazo<1,2-b>pyrazoles, 10, was unsuccessful.When the amide 2 had an N-phenyl-substituent the reduction gave an N-carbonyl cleavage followed by carbonyl reduction to amino alcohols 6a-d.When the amide 2 had N-methyl, N-tert-butyl, or N-2,6-dimethylphenyl as a substituent, then cleavage yielded an unusual formamide product, 9e-i.Further LiAlH4 treatment of 9e-h gave 10e-h by reductive ring closure of the iminium zwitterion 11e-f, 14g, or 14h by addition of hydride to theintermediate 11g or 11h and/or carbonyl cleavage to 13e or 13f.LiAlH4 treatment of 9i gave only 13i.Dehydrative ring closure of compounds 6a and 6b with P2O5 gave the products 10a and 10b.