Synthesis of new spirobenzazolines including a furo[3,4-b]pyran ring system

A series of 4,5-dihydrofuro3,4-b]pyran-6-spiro-2′-benzazolines 3 were prepared by reaction of 4,4-dimethyl-2,6-dioxo-4,5-dihydrofuro3,4-b]pyran 1 with o-phenylenediamine, o-aminophenol, o-aminothiophenol or their derivatives. Most of these compounds exhibited a significant analgesic activity.