1,3-Azaphospholo[5,1-a]isoquinolines

In a one pot synthesis, 1,3-azaphospholo[5, 1-a]isoquinoline (4) was obtain ed from the reaction of N-(alkoxycarbonylmethyl) isoquinolinium bromide (1) with PCI, in the presence of (C2H5)(3)N. A crossed reaction confirms the f ormation of 4 proceeding via a I, 5-electrocyclization. Compound 4 undergoe s [2 + 4] cycloaddition with 2, 3-dimethyl-1,3-butadiene in the presence of sulfur. The influence of the substituent group on the reactivity of the C = P - moiety in the 1,3-azaphospholo ring toward [2 + 4] cycloaddition is c orroborated by semiempirical PM3 calculations. (C) 1999 John Wiley & Sons, Inc.