Bis-3-oxo-lambda5-phosphole: isolation, structural analyses, and synthesis of phosphorus-ylide containing conjugated heterocycle.

A new class of phosphorus-ylide containing conjugate heterocycle was isolated from a mixture of colored products of the reaction of a silylphosphine and dimethyl acetylenedicarboxylate. The structure was determined and the selective synthesis was developed. The indigo-like bis-phosphole structure appears a green to blue color, which is derived from the low energy-gap of the phosphole.