Ruthenium–Porphyrin‐Catalyzed Diastereoselective Intramolecular Alkyl Carbene Insertion into CH Bonds of Alkyl Diazomethanes Generated In Situ from N ‐Tosylhydrazones

With a ruthenium–porphyrin catalyst, alkyl diazomethanes generated in situ from N ‐tosylhydrazones efficiently underwent intramolecular C(sp 3 )H insertion of an alkyl carbene to give substituted tetrahydrofurans and pyrrolidines in up to 99 % yield and with up to 99:1 cis selectivity. The reaction displays good tolerance of many functionalities, and the procedure is simple without the need for slow addition with a syringe pump. From a synthetic point of view, the CH insertion of N ‐tosylhydrazones can be viewed as reductive coupling between a CO bond and a CH bond to form a new CC bond, since N ‐tosylhydrazones can be readily prepared from carbonyl compounds. This reaction was successfully applied in a concise synthesis of (±)‐pseudoheliotridane.