1.5- Benzodioxepin-2-ones, synthesis

A highly regio- and stereo-regulated synthesis of the (Z)-l,4-benzodioxepin-5-ones 115 (Ar = Ph, 4-MeOC6H4 X = 0) has been reported, and involved, at the penultimate stage, cyclization of disubstituted alkynes on treatment with copper (I) iodide. <00JCS(P1)775>. 

A highly regio- and stereoselective synthesis of 3-arylidene-l,4-benzodioxepin-5-ones has been achieved with palladium-copper catalysis (Scheme 7) <2000J(P1)775>. 

This collection begins with a series of three procedures illustrating important new methods for preparation of enantiomerically pure substances via asymmetric catalysis. The preparation of 3-[(1S)-1,2-DIHYDROXYETHYL]-1,5-DIHYDRO-3H-2.4-BENZODIOXEPINE describes, in detail, the use of dihydroquinidine 9-0-(9 -phenanthryl) ether as a chiral ligand in the asymmetric dihydroxylation reaction which is broadly applicable for the preparation of chiral dlols from monosubstituted olefins. The product, an acetal of (S)-glyceralcfehyde, is itself a potentially valuable synthetic intermediate. The assembly of a chiral rhodium catalyst from methyl 2-pyrrolidone 5(R)-carboxylate and its use in the intramolecular asymmetric cyclopropanation of an allyl diazoacetate is illustrated in the preparation of (1R.5S)-()-6,6-DIMETHYL-3-OXABICYCLO[3.1. OJHEXAN-2-ONE. Another important general method for asymmetric synthesis involves the desymmetrization of bifunctional meso compounds as is described for the enantioselective enzymatic hydrolysis of cis-3,5-diacetoxycyclopentene to (1R,4S)-(+)-4-HYDROXY-2-CYCLOPENTENYL ACETATE. This intermediate is especially valuable as a precursor of both antipodes (4R) (+)- and (4S)-(-)-tert-BUTYLDIMETHYLSILOXY-2-CYCLOPENTEN-1-ONE, important intermediates in the synthesis of enantiomerically pure prostanoid derivatives and other classes of natural substances, whose preparation is detailed in accompanying procedures. 

Analogous to the synthesis of l,4-benzodioxepin-5-ones, the benzoxathiepinones (166) were prepared by the reaction of ethyl 2-thiobenzoates with chlorohydrin and glycerol chlorohydrin and cyclization of intermediate (165) (Scheme 17) <75BSF277>. The sodium borohydride reduction of bienzoxathiepinone (167) has also been studied <82NJC149>. 

Flavanones undergo a Baeyer-Villiger rearrangement to dihydro-l,5-benzodioxepin-2-ones on treatment with H2O2 and methyltrioxorhenium <01TL5401>. The synthesis of benzoxazepines from chromanones forms part of a review of the 7-membered ring compounds <01JHC1011>. 

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