Rearrangement of isoxazoline-5-spiro derivatives. 8. Selective formation of tetrahydropyridones from C,C-disubstituted nitrones

The thermal rearrangement of isoxazolidines 3, 7, 9, 17, and 19 obtained by 1,3-dipolar cycloaddition of C,C-disubstituted nitrones and methylenecyclopropanes 1 and 6 has been studied. The lack of hydrogen at the C-3 position of the isoxazolidine ring leads selectively to azaheterocyclic ketones, structurally differentiated according to the starting dipoles and dipolarophiles. The process allows the "one-pot" syntheais of valuable perhydro pyridone, indolizinone, and pprolo[1,2-a]quinolinone ring systems with excellent overall yield and atom economy. A new entry to the functionalized l-azaspiro[5.5]undee 22 framework found in alkaloids of the histrionicotoxin family is also presented.