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

[image omitted] 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 degrees C under solventless conditions. Cyclization of the intermediate (2) so obtained could be realized best under microwave conditions at 150 degrees 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.