Building blocks for phospha[n]pericyclynes

Reaction of i-Pr2NPCl2 with acetylenic Grignard reagents resulted in the formation of new acetylenic substituted phosphorus building blocks. These building blocks can be protected by forming the corresponding W(CO)5 complex and the double bond; length as m-dashO and double bond; length as m-dashS derivatives for added stability as was demonstrated for aminophosphine (11a). From this building block, very sensitive product mixtures containing tetraphospha[4]pericyclynes (16) were obtained. In addition, the amino-substituent of phosphines (11) could be removed upon treatment with HCl to give chlorophosphine (18) from which novel trisethynylphosphines (19) bearing different substituted alkynes were obtained that may serve as building blocks for novel three-dimensional phospha-acetylenic scaffolds such as the (di)ethynyl-expanded phosphacubanes 8 and 25 that, according to DFT calculations, have a higher degree of cyclic electron delocalization and reduced HOMO–LUMO gaps compared to their carbon-analogues.