Dioxepines—

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. 

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>. 

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-... 

Chlorine and bromine add normally to the double bond in (256) and the dibromo compound can be mono-dehydrobrominated using sodium methoxide in methanol to give a mixture of 5-bromo-4,7-dihydro-l,3-dioxepin and 5-bromo-4,5-dihydro-l,3-dioxepin (which is converted in situ to the 5-methoxy derivative). More interestingly it can be fully dehydrobrominated using HMPA at 140 °C to give the fully unsaturated 2H- 1,3-dioxepin (261) (76TL2113). This is the only known route to this compound. It gives a Diels-Alder adduct with 4-phenyl-l,2,4-triazoline-2,5-dione in 95% yield and on UV irradiation it isomerizes to (262). 

Dihydro-1,3-dioxepins (298) are prepared by the reaction of m-butene-1,4-diols with aldehydes, and a similar route gave the dithia derivative (299) which was converted into the more unsaturated compound (301) via (300) (76TL1251). 

Examples of 47i electrocyclization and related ring openings in oxygen-and sulfur-containing heterocycles have been widely reported. The effect of substituents on the ease of photocyclization of 1-benzoxepins (1) to cyclo-buta[b]-l-benzofurans (2) has been studied.3 1,3-Dioxepin (3) is readily converted to 2,4-dioxabicyclo[3.2.0]hept-6-ene (4) on irradiation in diethyl... 

Abundant recent work focused on the chemistry of benzo-fused derivatives, particularly on biaryl systems comprising a short tethered chain. A review on the chemistry of 1,3-dioxepins is available <2005PHC389>. 

Only a few reports have dealt with this type of synthesis of the 1,3-dioxepin and 1,3-dithiepin moiety. Dithiepane 148 could be obtained by an intramolecular transacetalization of mercaptane 147 (Scheme 40) <2000T10101>. 

The chiral substituted 1,3-dioxepine derivative 231 has been prepared in 96% ee (50% conversion) by an asymmetric Heck reaction with the alkene 229 and the aryl triflate 230 [01OL161 ]. 

Enantioselective isomerisation of the 4,7-dihydro-1,3-dioxepine 232 to (R)-(-)-233 has been achieved using (R,R)-(+)-CHIRAPHOS-(and (R,R)-(-)-Me-DuPHOS-) modified nickel complexes [01AG(E)177],... 

Dioxa-cycloheptene (2 H.4 H.7 H-1.3-Dioxepine) und ihre Mono-benzo-Derivate... 

Dioxepin 2-Chlormethyl-4,7-dihydro- E14a/1. 118 (Diol -f CH20)... 

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