Xepin

As reported by Shani and Sondheimer,1 the dehydrohalogenation of the tetrabromide by means of potassium hydroxide in ethanol at 50-55° affords a mixture, which is readily separated by chromatography on alumina, of l,6-oxido[10]annulene and the isomeric 1-benzo-xepin. The latter compound is also formed during chromatography of l,6-oxido[10]annulene on silica gel.7... 

Ogawa and co-workers37 have reported the synthesis of 6,7-benzo-4,9-epoxy[ 11]-annulenone 60. Manganese dioxide oxidation of the bis(hydroxymethylene)benzo-xepin 57 gave the dialdehyde 58 which on condensation with dimethyl acetonedicarb-oxylate 23 in chloroform in presence of piperidinium acetate gave the diester 59. This on hydrolysis followed by decarboxylation gave the annulenone 60. The NMR spec-... 

Substituted 5-methylene-l,3-dk>xepines 38 are converted into vinyl acetals 39 by Ni catalysts bearing (R,R)-DuPHOS or (R,R)-ChiraPHOS as chiral ligands (Scheme 11) [16]. Similarly high enantioselectivity can be achieved with 5-methyl-ene-l,3-dioxanes as substrates [17]. Chiral Ru-catalysts are less efficient [18]. Cyclic acetals obtained are an useful starting material for preparation of macrolide antibiotics and other polyketide-derived natural products. 

Decomposition of 4-diazomethyl-4//-pyrans 399 in the presence of a Pd(II) catalyst provides near quantitative yields of oxepins 400 (85CB3700) and 401 (87JOC3851). Analogously, in the yu-allylpalladium chloride-catalyzed decomposition of 2-diazomethyl-2//-l-benzopyrans 402, benzo-xepines 403 are formed via ring expansion in 50-78% yield (87CB1397). 

Thus, resolution of the TBS-proIccted o.xepin 54, conversion to the derived tilcohol and diastere-oselective alkylation with nBuMgBr affords (5 )-56 with >96% [Pg.279]

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