Synthesis of condensed isoxazolines and isoxazolidines via cycloaddition to furan-2(5H)-ones

Abstract

Cycloadditions of nitrone 1 and pyridylnitrile oxide 4 to furanones 2 and 3 afford tetrahydrofuro[3′,4′:4,5]isoxazolo[2,3-a]dibenzo[c,f]azepin- 1(3H)-ones and furo[3,4-d]isoxazolin-4(H)-ones, respectively, in a totally regioselective manner. The resulting adducts evolve into the corresponding pyrroloisoxazole systems by treatment with ammonium hydroxide and hydrazine hydrate in good yield. The N-O bond of isoxazolo[2,3-a]dibenzo[c,f]azepin-1(3H)- ones is not cleaved by LiAlH4.