Tandem Wolff rearrangement-“α-cyclization of tertiary amines” sequence: Synthesis of some 1H-2-benzopyran derivatives

Abstract The thermolyses of dimethyl 1-diazo-2-oxo(2-( N , N -disubstituted aminomethyl)phenyl)-ethylphosphonates 6a-e or the related ester 6f afford 1-disubstituted amino-1 H -2-benzopyran derivatives 9a-f through a 3-step sequence involving Wolff rearrangement, [1,5] hydride shift and subsequent ring closure. Compounds 9 can be easily transformed into 1-hydroxy-, 1-methoxy- or 1-thiophenoxy-1 H -2-benzopyran or isoquinoline derivatives by the action of various nucleophilic reagents. Extension of the reaction to some heterocyclic diazophosphonates analogous to 6 is also described.