1.4- Dioxepins

Perfluoro-2-methyl-2-pentene reacted with acyclic bifunctional nucleophiles such as 2-mercaptoethanol (89NKK1772) and ethylene glycol (86JAP61200983), in the presence of a base, to give 1,4-oxathiepin and dioxepin derivatives, respectively. Eight- and nine-membered heterocycles are obtained with 1,2-bifunctional benzenes such as salicyclic acid [81JFC(18)447]. 

Treatment of the 1,2-oxazines 52 with carbon monoxide at 1000 psi in the presence of cobalt carbonyl brings about insertion of carbon monoxide to form the 1,3-oxazepines S3 <96TL2713>. A convenient route to P-lactams fused to oxepines is made available by alkene metathesis. Thus reaction of 4-acetoxyazetidin-2-one with ally alcohol in the presence of zinc acetate, followed by iV-allylation of the nitrogen affords the derivative 54 which cyclises by RCM to form the oxazepinone 55 <96CC2231>. The same communication describes a similar synthesis of 1,3-dioxepines. 

Other polycarboxylates, such as Carbetimer, poly(maleic anhydride-co-cyclohexyl-l,6-dioxepin) and poly (maleic anhydride-co-4-methylpentenane), elicit a similar broad spectrum of activity. 

Lewis acid mediated [1,3] rearrangement of the 1,3-dioxepines 109 gave the trisubstituted tetrahydrofurans 110 in high yields and with generally high diastereoselectivities. The Lewis acids used included TiCf(7-PrO)2 and TBSOTf <06CC3119>. 

There are relatively few entries in the non-fused dioxepin area, and most of these focus on reactions of these systems. For example the triflic acid-initiated polymerisation of 1,3-dioxepane in the presence of acetic acid and hexanedicarboxylic acid has been studied and mechanistic aspects discussed <00JPS(A)1232>. Biodegradable microspheres for the controlled delivery of drugs have been made from copolymers and homopolymer blends of L-lactide and l,5-dioxepan-2-one <00PP1628>. Ring contraction of 5-methylene-l,3-dioxepanes (eg. Ill) on reaction with trimethylsilyl trifluoromethanesulfonate in the presence of base afforded the exo tetrahydropyrans, in good yields <00TL2171>. 

A 1,4-dioxepin fused derivative 122 of the anticancer agent acronycine was prepared by lead tetraacetate oxidation of c/.s-l,3-dihydroxy-l,2-dihydroacronycine followed by treatment with sodium borohydride <00NPL183>. 

The phosphine-phosphite BINAPHOS ligand was first used in the Rh-catalyzed asymmetric hydroformylation of heterocyclic olefins such as 2,5-dihydrofuran, 3-pyrroline derivatives, and 4,7-dihydro-1,3-dioxepin derivatives. It provided the optically active aldehydes as single products with enantioselectivity between 64-76% ee. In the hydroformylation of 2,5-di-... 

Dioxenes react, as expected, to produce thermally unstable dihalocyclo-propanes in high yield [51, 89]. Upon heating, the bicyclic system rearranges to yield the dichloromethyl-1,4-dioxene, whereas the tricyclic system, derived from the benzo-l,4-dioxene undergoes ring expansion to produce the benzo-1,5-dioxepin (Scheme 7.11). 

It is evident that 11, 12, and 13 can all be converted into their enantiomers by conceptual torsions about the bonds that link the starred atoms. The success of the operation does not depend on the number of ligands that are attached to these atoms, which constitute the terminal atoms of the lines of torsion (Fig. 3d, e, henceforth types d and e). Similarly, there is no place in this scheme for any restriction on dihedral angles a conceptual torsion can interconvert the stereoisomers of hexahelicene (8) or of dioxepin (7) (both type f, Fig. 3/) as readily as those of ordinary biphenyls (type d) with their perpendicular orientation of the rings. No idealization is required. 

Bismuth(III) Triflate-Catalyzed Synthesis of Dioxolanes, Dioxanes, and Dioxepines... 

This methodology was also applicable to the synthesis of dioxepines from aldehydes and cA-2-butene-l, 4-diol (Table 6). 

Scheme 14 Bismuth(III) triflate-catalyzed allylation of dioxepines followed by in situ derivati-zation to generate acetates...

Podgorski DM, Krabbe SW, Le L, Sierszulski PS, Mohan RS (2010) Bismuth compounds in organic synthesis. Synthesis of dioxanes, dioxepines and dioxolanes catalyzed by bismuth (III) triflate. Synthesis 2771-2775... 

It has been reported that 1 l//-dibenzo[h,< ][ ,4]dioxepin-l 1-one (dep-sidone) (243) undergoes photochemical decarboxylation and yields dibenzo-furan (59%) on irradiation with a high-pressure mercury lamp. The authors do not report whether the irradiation was conducted through silica or borosilicate glass. 

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