ZIOC researchers have proposed a new method for the synthesis of annelated oxazines

Derivatives of 1,2-oxazines are an important class of nitrogen-oxygen heterocycles widely used in organic chemistry. The structural fragment of 1,2-oxazine proved to be a convenient synthetic precursor for amino alcohols, functionalized carbonyl compounds, and a number of heterocycles: pyrrolidines, pyrroles, and furans. One of the key pathways for the synthesis of 1,2-oxazines is based on various transformations of six-membered cyclic nitronates. In a recent work, scientists from the Laboratory of Organic and Metal-Organic Nitrogen-Oxygen Systems of the Zelinsky Institute discovered a new reaction of [3+3]-annelation of nitronates with vinyldiazoacetates, leading to the formation of 6,6-annelated bicyclic nitrosoacetals. The transformation proceeds with the use of Rh(II) compounds as a catalyst and makes it possible to obtain target products in good yields and excellent diastereoselectivity. Under the action of a base, the synthesized nitrosoacetals undergo contraction of the unsaturated oxazine ring to the corresponding pyrrole. Both reactions can be performed in a one-pot mode, which is a fast approach to a rare type of heterocyclic structure containing a pyrrole-annelated oxazine ring from available starting compounds such as nitroalkenes, olefins, and diazo compounds.
 

Источник:

Yulia A. Antonova, Yulia V. Nelyubina, Sema L. Ioffe, Andrey A. Tabolin [3+3]-Annulation of Cyclic Nitronates with Vinyl Diazoacetates: Diastereoselective Synthesis of Partially Saturated [1,2]Oxazino[2,3-b][1,2]oxazines and Their Base-Promoted Ring Contraction to Pyrrolo[1,2-b][1,2]oxazine Derivatives // Molecules 2023, 28, 3025. DOI: 10.3390/molecules28073025.