Organocatalyzed Phospha-Michael Addition: A Highly Efficient Synthesis of Customized Bis(acyl)phosphane Oxide Photoinitiators

Addition of the P-H bond in bis(mesitoyl)phosphine, HP(COMes)(2) (BAPH), to a wide variety of activated carbon-carbon double bonds as acceptors was investigated. While this phospha-Michael addition does not proceed in the absence of an additive or catalyst, excellent results were obtained with stoichiometric basic potassium or caesium salts. Simple amine bases can be employed in catalytic amounts, and tetramethylguanidine (TMG) in particular is an outstanding catalyst that allows the preparation of bis(acyl)phosphines, R-P(COMes)(2), under very mild conditions in excellent yields after only a short time. All phosphines RP(COMes)(2) can subsequently be oxidized to the corresponding bis(acyl)phosphane oxides, RPO(COMes)(2), a substance class belonging to the most potent photoinitiators for radical polymerizations known to date. Thus, a simple and highly atom economic method has been found that allows the preparation of a broad range of photoinitiators adapted to their specific field of application even on a large scale.

Automated summary

A simple and highly atom economic method has been found for preparing a wide range of photoinitiators adapted to specific fields of application. This method involves the addition of bis(mesitoyl)phosphine to activated carbon-carbon double bonds, using basic potassium or caesium salts as additives. Simple amine bases can also be used as catalysts, with tetramethylguanidine being a particularly outstanding catalyst.