Unprecedented base-promoted nucleophilic addition of diazoesters to nitrones

Exploring the Metal‐Catalyzed Reactions of α‐Diazo‐β‐hydroxyamino Esters: Conversion of Cyclic Aldonitrones into Ketonitrones

“…The transformation of diazo compounds 3 and 4 in the presence of metal catalysts was thus investigated. In a preliminary communication, we reported a ring‐expansion reaction arising from the treatment of cyclic diazohydroxylamines 4 with catalytic amounts of metal complexes,[2b] similar to published ring‐expansion reactions of diazopyrrolidines and diazopiperidines . However, we have recently obtained unambiguous evidence that the structures of the products resulting from these reactions were erroneously assigned, and that a 1,2‐hydride shift is favored over the initially proposed ring expansion.…”

“…The starting material was rapidly consumed at room temperature to give a major product (53 %), which was assigned as ring‐expanded nitrone 6 , based on the previous transformation of 3a into 5 (Scheme ). [2b] However, while studying potential synthetic applications of nitrone 6 we discovered that the initial structural assignment was incorrect: reduction of this nitrone with LiAlH 4 gave a crystalline alcohol 7 . Crystallographic analysis of this compound unambiguously revealed the presence of a five‐membered ring .…”

“…We thus had to revise the structure of nitrone 6 to nitrone 8 and also revise the structures of all the congeners reported in our initial publication. [2b]…”

“…We have recently described an efficient synthesis of α‐diazo‐β‐hydroxyamino esters by the addition of lithiated α‐diazoesters to acyclic and cyclic nitrones (Scheme ) . In particular, from cyclic nitrones 2 , the corresponding diazohydroxylamines 4 were obtained in high yields and, in most cases, with excellent diastereoselectivities.…”

Recent Advances in the Preparation of Enantiomerically Pure Hydroxylamines from Nitrones

“…Similar results were observed with C-furanosyl nitrones (dr 3:2). [61] On the other hand, the addition to cyclic nitrones proceeded quantitatively and with complete selectivity, only one isomer being isolated from the reaction mixture. [62] The addition of a lithiated purine to cyclic nitrones also proceeded with total selectivity.…”