Seven-membered systems containing three or more heteroatoms

4 SEVEN-MEMBERED SYSTEMS CONTAINING THREE OR MORE HETEROATOMS 

It was reported that cyclic dialkoxy disulfides 171 undergo ring contraction to a thionosulfite 172 followed by extrusion of sulfur to give the sulfoxylate 173 and the mechanism of these transformations discussed 07JOC3906 . 

The highly oxygenated bicyclic trioxepine 176 was synthesised by photo-oxygenation of an allylic alcohol 174 followed by peroxylacetalisation of 175 with trimethyl orthoacetate 07AG(E)8883 . 

Reagents (i) 02, hv.TTPB, CCI4, 10°C (ii) CH3C(OMe)3, PPTS, CH2CI2 

Heteropolyacids have been used as recyclable catalysts in the reaction between ortho-phenylenediamines 180 with acid chlorides to yield 1,3,5-benzoxadiazepines 181 in good yield 07MOL255 . 

An elegant use of bis-acetylenic ketones (e.g. 213) in the synthesis of 1,2,4-triazepines 216 and 217 has been described 05JOC3307 . The ring heteroatoms are introduced in a one pot reaction with 213 and 214 followed by conversion of the pyrimidine intermediate 215 to 216 and 217 on reaction with trifluoroacetic acid. In contrast, reaction of 215 with TBAF gave the 

The unusual sila sultones (222, R = Me, Bu) can be accessed readily in moderate yields by cyclisation with dehydration of the appropriate siloxane disulfonic acid precursor 05T7233 . 

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