1.2.4- Dioxazolidines

Following a report by Biichi and Ayer > on the photolysis of nitrobenzene in cyclohexene and 2-methyl-2-butene, a thorough study on nitrobenzene cycloaddition to olefines has been undertaken by de Mayo and co-workers 3 . ). Evidence was presented for the previously postulated ) formation of 1,3,2-dioxazolidines ... 

A twisted envelope conformation with N as flap was deduced for 1,3,2-dioxazolidine (30 R = = H) from the AA BB spectrum of the ring protons combined with an isochronism... 

Dioxazolidines are obtained by the intramolecular acid-catalyzed cyclization of N,N-di-alkoxyamines (preformed or produced in situ) or by cyclization of N-chloro-N-alkoxyamines (Scheme 11 <8HZV2539,87IZV1556) and Scheme 12 <89KGS393 . 

Dioxazolidines are produced by cyclization of A,A-dialkoxy- or A -alkoxy-A -chloroamines (Scheme 11) <93CRV725>. The synthetic potential of this method far surpasses that of the photochemical addition of nitrobenzene to alkenes <84CHEC-1(6)-914). 

The photochemical action of nitrobenzene on unsaturated compounds in sunlight is a field already investigated by Vechiotti and Zanetti.295 Recently, Buchi and Ayer32 have evaluated the reaction of nitrobenzene with olefins as a possible synthetic route to the heterocyclic class of compounds, 1,3,2-dioxazolidines (CXLVI). Photoexcited... 

The main structural types of the azoles are given in Figure 1. Most of them are experimentally available and stable at room temperature. The basic parent structures are shown in row A and named as 1,3,2-dithiazoles, 1,3,2-dithiazolidines, 1,3,2-dioxazoles, and 1,3,2-dioxazolidines. Row B represents the known 1,3,2-dithiazolium and dithiazolidinium cations and 1,3,2-dithiazolyl and 1,3,2-dithiazolidinyl radicals, respectively. 

Reactions of hydrogenated derivatives including fluorination of disulfonimides and oxidation 1,3,2-dioxazolidines was an important subject considered in CHEC-II(1996) <1996CHEC-II(4)433>. 

Synthesis of unsubstituted derivatives by hydrolysis of N-substituted 1,3,2-dioxazolidines has been the main subject for investigation in this area <1996CHEC-II(4)433>. 

Condensed 1,3,2-dioxazoles are produced by the reaction of A-phenyliminophosphorane and 9,10-phenanthreno-and 1,2-naphthoquinones (Scheme 7). Photochemical addition of tetranitromethane to aromatic compounds is still in use for the preparation of 1,3,2-dioxazolidines 22 and 23 but in low yields. 

Other intramolecular cyclizations accompanied by elimination are the preparation of the l,2,4-dioxazolin-3-ones (190) by HC02H dehydrative cyclization of a precursor percar-bamic acid (72JPR145) formation of the l,3,4-dioxazol-5-ones (191) from the hydroxamic ester (192) (78JAP78127479) and preparation of the 1,3,2-dioxazolidine (57) by base treatment of the precursor A-methoxy-A-hydroxyethoxy compound (80IZV2181). 

Cycloaddition. Nitrobenzene can undergo cycloaddition to a strained alkene such as (Z,E)-l,5-cyclooctadiene (1) to form a 1,3,2-dioxazolidine (2). The reaction proceeds in THF at room temperature over a period of 5 days. The adducts are formed more rapidly and in higher yield when the benzene ring... 

---