Synthesis of 6-hydroxymethyl-5,6-dihydro-4H-1,2-oxazines by one-pot-cyclization of dilithiated oximes with epibromohydrin

Small and Smart: Adventures in Epihalohydrin Chemistry

The present personalized account aims to highlight reactions of epichlorohydrin and epibromohydrin with free and masked dianions. These reactions permit convenient syntheses of a variety of products, such as 2-(alkylidene)tetrahydrofurans (which can be further functionalized by hydrogenation or ring-transformation reactions), cyclopropanes, γ-butyrolactams, oxazines, oxazolo[3,4-b]pyridazin-7-ones, or 2-(alkylidene)thiazolidines. In general, the reactions proceed with very good regioselectivity.

1 Introduction

2 Reactions of Masked Dianions

2.1 Synthesis of 2-(Alkylidene)tetrahydrofurans

2.2 Functionalization of 2-(Alkylidene)tetrahydrofurans

3 Reactions of Free Dianions

3.1 Synthesis of 2-(Alkylidene)tetrahydrofurans

3.2 Functionalization of 2-(Alkylidene)tetrahydrofurans

3.3 Synthesis of γ-Butyrolactams

3.4 Synthesis of 5,6-Dihydro-4H-1,2-oxazines

3.5 Synthesis of Oxazolo[3,4-b]pyridazin-7-ones

3.6 Synthesis of Cyclopropanes

3.7 Synthesis of 2-(Alkylidene)thiazolidines

4 Conclusions

Diastereospecific Gold(I)-Catalyzed Cyclization Cascade for the Controlled Preparation of N- and N,O-Heterocycles

The reaction of oxime-tethered 1,6-enynes with a cationic gold(I) catalyst demonstrates a great potential for the synthesis of a range of heterocycles in a diastereospecific fashion. The control of the configuration of the oxime and the alkene of the enyne moiety is the key to selectively obtain dihydro-1,2-oxazines, isoxazolines or dihydropyrrole-N-oxides as single diastereoisomers. As supported by DFT calculations, these cascade reactions proceed stepwise, by the intramolecular addition of the O or N atom of the oxime onto cyclopropyl gold(I) carbene intermediates. In this study, a rare [3,3]-sigmatropic rearrangement of nitrones is also observed.

One-Pot Cyclizations of Dilithiated Oximes and Hydrazones with Epibromohydrin. Efficient Synthesis of 6-Hydroxymethyl-5,6-dihydro-4H-1,2-oxazines and Oxazolo[3,4-b]pyridazin-7-ones

The one-pot cyclization of dilithiated oximes with epibromohydrin provided a convenient and regioselective approach to 6-hydroxymethyl-5,6-dihydro-4H-1,2-oxazines. The reaction of the latter with phosphorus tribromide resulted in a Beckmann rearrangement and formation of 5-bromomethyl-2-iminotetrahydrofurans. The reaction of dilithiated hydrazones with epibromohydrin afforded oxazolo[3,4-b]pyridazin-7-ones, which were formed by a novel domino cyclization.