Copper-mediated rearrangements 2,3 -rearrangement

The final sequence for conversion of the product from steps 1-1-8 to baccatin III begins with a copper-mediated allylic oxidation and also involves an allylic rearrangement of the halide. The exocyclic double bond was then used to introduce the final oxygens needed to perform the oxetane ring closure. 

Various functionalized alkynes can be submitted to carbocupration reactions, such as alkoxyalkynes,150 alkynyl carbamates,151 acetylenic orthoesters,152 and thioalkynes.153 The carbocupration of orthoesters, for example, 204, has been used to prepare a-substituted esters of the type 206 by acidic hydrolysis of the adduct 205 (Scheme 51).152 This allows the formation of regioisomers that are not accessible by copper-mediated addition to acetylenic esters. A stereoselective synthesis of trisubstituted alkenes has been described by Normant et al.lSd> starting from phenylthio-acetylene 207. Carbocupration with lithium di- -butylcuprate affords the intermediate 208 which, upon addition of /z-butyllithium, undergoes a 1,2-metalate rearrangement to the vinylcuprate 209. The latter can be trapped with various electrophiles, for example, ethyl propiolate, providing product 210 with complete regio- and stereocontrol. 

Benzothiepines 69 have been synthesised by a gold-catalysed rearrangement of homopropargyl arylsulfoxides 68 <07JACS4160>. The dibenzothiepine 71 was synthesised by intramolecular Friedel-Crafts acylation of a diarylsulfide 70 which was formed by the copper mediated substitution of an appropriately substituted aryl derivative with thiophenol... 

The metal-catalyzed decomposition of diazo compounds 603 provides access to a variety of cephem derivatives (Scheme 30). Copper-mediated cyclization of diazo ketone 603 (R = Et) gives 3-oxocepham through sulfo-nium ylide formation followed by j8-elimination (80H1999). The formation of cephem derivatives 604 and 605 presumably involves the intermediacy of ylide 606 (R = Ac, ArCH2) and its subsequent rearrangement. A more sophisticated mechanism is proposed for the formation of 607 and 608 (83H205). 

Julian, R. R., May, J. A., Stoltz, B. M., Beauchamp, J. L. Gas-Phase Synthesis of Charged Copper and Silver Fischer Carbenes from DIazomalonates Mechanistic and Conformational Considerations In Metal-Mediated Wolff Rearrangements. J. Am. Chem. Soc. 2003, 125, 4478 486. 

Sulfonium ylides have also been generated by reactions involving carbenoids. Copper-mediated decomposition of ethyl diazoacetate in the presence of the dithiane (387) led to the intermediate ylide (388), which then rearranged to yield a mixture of the betweenanene (389) and the (Z)-alkene (390) in a 3 1 ratio (Scheme 61) <84TL3555>. 

The oxyarylation of alkenyl boronic acids with 7V-arylbenzhydroxamic acids occurs with both copper-mediated and copper-catalysed conditions to give Fischer-indole intermediates. This transformation proceeds through a copper-promoted C-0 bond-forming event followed by a [3,3]-rearrangement (Scheme 7). 

The synthesis of a-imino aldehydes through the thermal [l,3]-rearrangement of 0-alkenyl benzophenone oximes has been reported. A copper-mediated C-O bond coupling between benzophenone oxime and alkenyl boronic acids provides access to 0-alkenyl oximes and a Horner-Wadsworth-Emmons olefination applied to the a-imino aldehyde products gives y-imino-a, -unsaturated esters (Scheme 166). ... 

Copper(II) acetate has been reported as a versatile catalyst for the transformation of aldehydes into primary amides with hydroxylamine. A route to dibenzoxazepinones from 2-iodobenzamides and 2-bromophenols has been reported to involve a copper-catalysed Ullmann coupling followed by a base-mediated Smiles rearrangement and ring-closing process (Scheme 104). " ... 

Iron(II) salts, usually in conjunction with catalytic amounts of copper(II) compounds, have also been used to mediate radical additions to dienes91,92. Radicals are initially generated in these cases by reductive cleavage of peroxyesters of hydroperoxides to yield, after rearrangement, alkyl radicals. Addition to dienes is then followed by oxidation of the allyl radical and trapping by solvent. Hydroperoxide 67, for example, is reduced by ferrous sulfate to acyclic radical 68, which adds to butadiene to form adduct radical 69. Oxidation of 69 by copper(H) and reaction of the resulting allyl cation 70 with methanol yield product 71 in 61% yield (equation 29). 

Decarboxylation of 5,7-dimethyl-8-oxo-6-aza-8//-indeno[2,1 - ]thiophene-4-carboxylic acid could be effected by heating an admixture of it and copper powder <87H(26)1535). Direct sublimation in vacuo afforded the desired product (58%). 9-Chloro-2- and 3-methyltriazolo[4,5-/]quinoline-7-carboxylic acids are decarboxylated under similar conditions <93H(36)259>. The cyano group of 8-cyano-7-oxo-4,5,6,7-tetrahydrothiazolo[4,5-/]quinolines can be converted into an amino group by cone. HC1 mediated hydrolysis to the amide, followed by Hofmann rearrangement <89H(29)I517>. 

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