4‑Diazoisochroman-3-imines: A Class of Metal Carbene Precursors for the Synthesis of Isochromene Derivatives

4-Diazoisochroman-3-imines were investigated for their synthetic applications as a new class of metal carbene precursors. Under the catalysis from a Rh­(II) complex, this class of α-diazo imidates reacted with alkenes and conjugated dienes through a formal [2 + 1] (i.e., cyclopropanation) or [4 + 3] cycloaddition to furnish spiro­[cyclopropane-1,4′-isochroman]-3′-imines and tetrahydroisochromeno­[3,4-b] azepines, respectively. When Rh­(II)/AgOTf was used as cocatalyst, the formal [3 + 2] cycloaddition of 4-diazoisochroman-3-imines with terminal alkynes took place, leading to the synthesis of 2-aryl-3,5-dihydroisochromeno­[3,4-b]­pyrroles.