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By Favorskii rearrangement

The methyl ester (100, R = CH3), derived from this A-nor acid by treatment with diazomethane, is different from the ester (102) obtained either by Favorskii rearrangement of 2a-bromo-5a-cholestan-3-one (101) or by the action of cyanogen azide on 3-methoxy-5a-cholest-2-ene (103) followed by hydrolysis on alumina. The ketene intermediate involved in photolysis of (99) is expected to be hydrated from the less hindered a-side of the molecule to give the 2j -carboxylic acid. The reactions which afford (102) would be expected to afford the 2a-epimer. These configurational assignments are confirmed by deuteriochloroform-benzene solvent shifts in the NMR spectra of esters (100) and (102). ... [Pg.441]

The reaction of a polyhalo ketone with base (equation 3) was described several years before Favorskii described a similar rearrangement (equation 4). Simple a,a- and a,a -dihalo ketones yield the same product (Scheme 14), so dibromination can be followed by Favorskii rearrangement without purification. These rearrangements are usually stereospecific, though subsequent cis to trans isomerization, under the influence of base, often obscures this feature. Various explanations have been provided for this stereospecificity, but the one due to Rappe (illustrated in Scheme 15) seems most plausible. ... [Pg.843]

The second stage of the synthesis of all-czs-fenestrindane 9 begins by contraction of the cyclohexanone ring of 227 by two-fold bromination followed by Favorskii rearrangement [93] (Scheme 46). Subsequent decarboxylation of the acrylic acid furnishes the all-czs-tribenzo[5.5.5.5]fenestrene 233 in moderate overall yield. This compound as well as the precursors 225 and 227 have been converted into a number of related fenestranes including all-ds-tribenzo-... [Pg.204]

Sodium/alcohol Ring contraction by Favorskii rearrangement... [Pg.230]

The iridane part of jasminin has been synthesized. Mild alkaline hydrolysis of jasminin gave the triol (337). Synthesis of (337) was effected by Favorskii rearrangement of ( + )-carvone epoxide (338) which gave the parent acid of the ester (339) in 20 % yield. The assignment of the configuration of hydroxyl is based both on mechanistic grounds and on n.m.r. evidence [J(4,5a) = 5 Hz, J(4,5p) = 5 Hz, J(3,4) = 6 Hz]. Hydroboration of (339) lead directly to the desired triol (337). [Pg.237]


See other pages where By Favorskii rearrangement is mentioned: [Pg.762]    [Pg.1921]    [Pg.220]    [Pg.334]    [Pg.352]    [Pg.228]    [Pg.362]    [Pg.98]    [Pg.118]    [Pg.183]   
See also in sourсe #XX -- [ Pg.1403 , Pg.1647 ]




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