Cyclopentanes from N‐Aminoglyconolactams: Reaction Mechanism and Improved Access to Diazocyclopentanones

Abstract

AbstractOne of the two mechanisms to rationalize the Pb(OAc)4 oxidation of 1 to 2 and 3 postulates the intermediate generation of a carbene 25 via the acetoxy‐diazepinone 22 and the oxadiazoline 23 (Scheme 2). This mechanism was excluded on the basis of the oxidation of the diazepinone 32 that was synthesized in six steps from the ribonolactone 26. Oxidation of 32 with Pb(OAc)4 provided the unstable acetoxy‐diazepinone intermediate 22, its C(5) epimer, and the stable 5‐O‐acetyl‐1,5‐ribonolactone 33; the 1H‐NMR spectra of the products of the oxidation of 32 and the decomposition of 22 showed no evidence for the formation of the acetoxy epoxide 2 and the diazo ketone 3, excluding 22 as intermediate in the oxidation of 1. To increase the yield of the diazo‐cyclopentanones, we oxidized the acetohydrazide 34, the 4‐toluenesulfonohydrazide 44, and the N,O‐diacetate 46 with Pb(OAc)4. Oxidation of the acetohydrazide 34 with Pb(OAc)4 led to a higher yield of the diazo ketone 3 (40%) than oxidation of the N‐amino‐ribonolactam 1 without affecting the yield of 2. Oxidation of the 4‐toluenesulfonohydrazide 44 gave mostly the product 45 of C‐acetoxylation, while the analogous oxidation of 46 gave the acetoxy lactone 33; neither 2 nor 3 could be detected among the products, excluding 46 as intermediate of the oxidation of 34. Oxidation of the N‐acetamido‐lyxonolactam 47 with Pb(OAc)4 provided the diazo ketone 8 (77 vs. 37% from 5); higher yields of diazo ketones resulted also from the oxidation of the acetohydrazides 48 and 49.