Microwave-promoted syntheses of fluoren-9-ones and benzisoxazoles

Synthesis of some new fluoren-9-ones and benzisoxazoles under both thermal and microwave conditions is reported. The prepared products under microwave conditions are obtained with high yields and within shorter reaction times. Reaction of lithiated bromobenzene with aromatic aldehydes 2a , b delivered diarylmethanols 3a , b that were oxidized to 4a,b . Compound 4a was cyclized to give methoxyfluoren-9-one 5, which was demethylated affording hydroxyfluoren-9-one 6 . Compound 4b was reacted with triethyl phosphite to produce benzisoxazole 10 . On the other hand, reaction of triethyl phosphite with 13a,b afforded a mixture of phosphoramidates 14a,b and benzisoxazoles 15a,b . The structures of the synthesized compounds have been elucidated unambiguously by NMR-spectroscopic methods including HH COSY, HSQC, and HMBC experiments.