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 stating dipoles and dipolarophiles. The process allows the "one-pot" synthesis of valuable perhydro pyridone, indolizinone, and pyrrolo[1,2-a]quinolinone ring systems with excellent overall yield and atom economy. A new entry to the functionalized 1-azaspiro[5.5]undecane 22 framework found in alkaloids of the histrionicotoxin family is also presented.