Preparation of 7-Methylenepyrrolo[l,2-c]pyrimidin-l(5H)-ones and their 1,3-Dipolar Cycloadditions towards Isoxazolinyl and Isoxazolidinyl Spironucleosides

摘要

Novel 6,7-dihydro-5-hydroxy-3-methoxy-7-methylenepyrrolo[l,2-c]pyrimidin-l(5.ff)-ones were prepared from orotic acid. Their 1,3-dipolar cycloadditions with mesitonitrile oxide and methoxycar-bonyl nitrone proceed with complete regioselectivity, the approach of the dipole taking place predominantly from the less sterically hindered side of the dipolarophiles. The isoxazolidinyl spironu-cleoside, bearing a primary hydroxyl group on methyl in C-3 position of the isoxazolidinyl ring, was prepared in three steps from the major isoxazolidine.