Practical Synthesis of 6-Chloro-dibenzo[c.e][1,2]oxaphosphorine

Abstract

The title P-heterocycle 3, a versatile intermediate in synthesis, was prepared by two independent methods. The first involves an environmentally friendly version of an old protocol starting from 2-phenylphenol (1) and phosphorus trichloride. Their interaction could be accomplished at 50 °C under solventless conditions. Cyclization of the intermediate (2) so obtained could be realized best under microwave conditions at 150 °C in the presence of ZnCl₂. This method offers advantages over the traditional ones. According to another approach, the chloro-dibenzooxaphosphorine (3) was obtained by the novel reaction of 6H-dibenzo[c.e][1,2]oxaphosphorine-6-oxide (4) with phosphorus trichloride in boiling chloroform. Efficiency of the syntheses was demonstrated by converting the crude product 3 to a more stable phosphonic amide (6) that was stable enough to be isolated.

Keywords:

• Cyclization
• dibenzo[c.e][1,2]oxaphosphorine
• microwave
• substitution

ACKNOWLEDGMENTS

This above project was supported by the Hungarian Scientific and Research Fund (OTKA K067679 and K83118). The authors are grateful to Dr. Harry R. Hudson (London Metropolitan University) for his advice.