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Volumn 5, Issue 6, 2014, Pages 2416-2421

Copper catalyzed Heck-like cyclizations of oxime esters

Author keywords

[No Author keywords available]

Indexed keywords

COPPER; CYCLIZATION; ESTERIFICATION; ESTERS;

EID: 84900303367     PISSN: 20416520     EISSN: 20416539     Source Type: Journal    
DOI: 10.1039/c4sc00652f     Document Type: Article
Times cited : (137)

References (53)
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    • Pentafluorobenzoyl oxime esters are usually employed for these processes because they are stable to Beckmann rearrangement Imino-Pd(ii) intermediates have been characterized and exploited in catalytic C-H amination
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    • Previous studies are consistent the direct insertion of the alkene component into the N-Pd(ii) bond in a manner that is analogous to the conventional Heck reaction (see ref. 6b and c)
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    • These processes are proposed to involve oxidative addition of Cu(i) into the N-O bond. For mechanistically similar processes that involve O-acyl hydroxylamine derivatives, see
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    • The mechanism for nitrile formation is not clear. Possible pathways include (but are not limited to) Lewis acid promoted Beckmann type-II rearrangement of the oxime ester or β-hydride elimination from an imino-Cu(iii) intermediate (vide infra). See also ref. 9a Addition of molecular sieves to the reaction mixture did not suppress the formation of this byproduct. Consequently, we favor a pathway involving decomposition of the oxime ester to the corresponding NH-imine and hydrolysis to the ketone during work-up or chromatography. The NH-imine may form via either an imino-Cu(iii) intermediate or an iminyl radical (vide infra) For a review on the one electron reduction of oxime derivatives, see
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    • Iminyl radical and imino-Cu(iii) intermediates may exist in equilibrium as depicted in Scheme 2A. Imino-Cu(iii) intermediates have been proposed previously (for example, see ref. 9a and b). An alternative possibility is that a radical anion of the oxime ester is generated which then cyclizes, with concomitant loss of pivalate, to generate an alkyl radical (see ref. 11i)
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    • Exposure of the analogous O-pentafluorobenzoyl oxime ester to our optimized Pd-based systems (see ref. 6) did not result in the formation of 8n or products related to 34 and only formal hydrolysis to the corresponding ketone was observed. See ref. 6a for a discussion on mechanistic pathways to the ketone
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