Pinacol coupling reactions intermolecular

As expected with a reagent that is csq)able of generating ketyls, intermolecular pinacolic coupling reactions can also be carried out with considerable efficiency using Smh. Treatment of aldehydes or... 

Dicyclopentadienylsamarium also promotes intermolecular pinacolic coupling reactions with exceptional efficiency.Both benzaldehyde and acetophenone are reported to undergo coupling very rapi y at room temperature in the presence of this reductant. After hydrolysis, pinacols are isolated in virtually quantitative yields. 

Shikonin. Torii has accomplished an efficient intermolecular pinacol coupling reaction, en route to the total synthesis of shikonin, a compound with antiinflammatory, antibacterial, and antitumor activity (Eq. 3.11) [29], Because the aromatic aldehyde possessed a substituent capable of chelating to vanadium, Torii anticipated, based on precedent, that selective cross-coupling would be possible. The pinacol reaction proceeded in 73% yield and with good diastereoselectivity (5.5 1). 

From a synthetic standpoint the intermolecular pinacolic coupling reaction is limited because only homocoupling reactions are generally practical. Cross-coupling reactions mediated by SmF are restricted to specialized, matched partners [35]. Thus a-dicarbonyl compounds can be heterocoupled with aldehydes, providing facile entry to 2,3-dihydroxy ketones. Although selectivities vary, in some cases the diastereoselectivity of the process can be quite high (Eq. 25). 

In analogy to intermolecular pinacolic coupling reactions, organometallic dialdehydes have served as precursors for the intramolecular version of the reaction, affording cyclic 1,2-diols [39]. Both arene chromium tricarbonyl (Eq. 29) and ferrocene complexes (Eq. 30) afford excellent yields of the desired products. 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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