BIS(PHOSPHINO)CARBODIIMIDE - A BIS(1,3)-DIPOLE

Bis[bis(diisopropylamino)phosphino]carbodiimide (1) reacts with 1 equi v of dimethyl acetylenedicarboxylate affording the [3 + 2] cycloadduct 2 in 92% yield, showing that a phosphinocarbodiimide acts as a 1,3-di pole. Addition of a second equivalent of alkyne to 2 gives rise to the formal [2 + 7] cycloadduct 5 in 85% yield. Migration of a carbomethox y group is observed on thermolysis of 5 at 80 degrees C, leading to a new bicyclo[4.3.0] derivative 7 in 90% yield. The X-ray diffraction st udy of derivatives 5 and 7 is presented. The mechanisms rationalizing the formation of 2, 5, and 7 are discussed.