Further studies in the photorearrangement of heterocyclic nitroalkenes;1 a facile synthesis of 6-hydroxy-1,2-oxazines

Conjugated Nitrodienes. Synthesis and Reactivity

“…Next, compound 209 was photodimerized to cyclobutane 210 by irradiation with a Hanovia medium-pressure mercury arc (Scheme ). This process has been used to synthesize fused 6-hydroxy-1,2-oxazines from heterocyclic nitroalkenes; thus, as indicated in Scheme , irradiation of 2-(2-nitroprop-1-enyl)benzofuran ( 211 ) in an acetone solution yielded the 6-hydroxy-1,2-oxazine ( 212 ), with analogous rearrangements observed to their corresponding oxazines with 2-(2-nitroprop-1-enyl)furan and its 5-methyl derivative and with 2-(2-nitroprop-1-enyl)indole. , …”

Unique Michael Addition-Initiated Domino Reaction for the Stereoselective Synthesis of Functionalized Macrolactones from α-Nitroketones in Water

“…In this context, we have recently shown that α-nitroketones 1 react with unsubstituted α,β-unsaturated aldehydes and ketones in water at room temperature, giving the expected Michael adducts, which could also be obtained using dilute potassium carbonate as the reaction medium if the reaction times were kept short enough to prevent opening of the nitroketone moiety by a retro-Claisen-type mechanism. However, in the case of the more hindered α,β-unsaturated aldehydes bearing an alkyl group at their α position, the reaction did not take place in the absence of catalyst, and addition of base led to an abrupt change in the course of the reaction, since the products were bridged bicyclic lactones 3 bearing an unusual 6-hydroxy-1,2-oxazine ring (Scheme ). As shown in Table , the reaction was very versatile in terms of the size of the starting material, and therefore it could be applied to the fast preparation of functionalized macrolactones of various ring sizes.…”