13C NMR study of isoxazolines and isoxazolidines in the thiophene and benzo[b]thiophene S-oxide and S,S-dioxide series

The ¹³C NMR spectra were recorded for isoxazolines and isoxazolidines from 2,4,6-trimethylbenzonitrile oxide or α-phenyl-N-phenyl nitrone as dipolarophiles with the thiophene and benzob]thiophene S-oxide and S,S-dioxide series. The effects of the isoxazoline or isoxazolidine groups are not very different. Owing to the electronegativity of the oxygen atom, the main influence arises from the regioselectivity of the addition to the carbon atoms located at the α or β position from SO or SO₂.