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Cyclopentanes from N ‐Aminoglyconolactams: Reaction Mechanism and Improved Access to Diazocyclopentanones
Author(s) -
Hu Guixian,
Vasella Andrea
Publication year - 2004
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200490218
Subject(s) - chemistry , diazo , yield (engineering) , ketone , medicinal chemistry , epimer , decomposition , epoxide , carbene , organic chemistry , catalysis , materials science , metallurgy
One 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 1 H‐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 .