Regioselective coupling

The best conditions for the a-regioselective coupling of a chiral, highly substituted, lithiated allyl sulfide to a chiral aldehyde were carefully worked out for the key step in an erythronolide B total synthesis108. 

Enynes are also especially effective in regioselective couplings, and the ligand structure and stoichiometry were both found to be important variables (Scheme 14) [31]. A model was proposed involving stereospecific ligand sub-... 

The Lipomannan Component of LAM Regioselective Couplings with NPOEs The... 

Cathodic reduction of retinal leads to a regioselective coupling in the presence of malonic ester to produce the corresponding pinacol (Fig. 26) [129]. Chromium(III) ions facilitate the reduction and favor the regioselective coupling of conjugated dienones to pinacols. A Cr(III)-carbonyl compound complex is evidenced as the reason for the selectivity [130]. 

The related lithium(phenylthio)cyclopropylcuprate, prepared from cyclopropyllithium and PhSCu, has been extensively used in the synthesis of /1-cyclopropyl enones by coupling with the corresponding fl-iodo enones (equation 10)34 36. Repetitive regioselective coupling of ethynylcyclopropane units by this method led to polyspirocyclopropyl acetylenes as precursors to [NJpericyclynes37. 

A highly regioselective amination of 6-aryl-2,4-dichloropyrimidines has been developed using palladium catalysis. The reaction which works well with secondary aliphatic amines and with anilines gives the 4-substituted products.46 Palladium catalysis has also been used in the regioselective coupling of 2,3-dibromopyridine with a series... 

As mentioned earlier, proteases have been extensively studied to carry out resolutions both of natural and unnatural amino acids. These useful reactions provide chiral compounds, which very often cannot be obtained by chemical means. The use of proteases to carry out enantioselective and regioselective coupling reactions, especially incorporating the use of organic solvents, has provided numerous examples of synthetic and semi-synthetic peptides.211-218... 

Hypervalent iodine(lll) was shown to catalyze the direct cyanation of iV-tosylpyrroles and -indoles under mild conditions, without the need for any prefunctionalization <2007JOC109>. Phenyliodine(m) bis(trifluoroacetate)-induced oxidative regioselective coupling of pyrroles in the presence of bromotrimethylsilane gave a series of electron-rich bipyrroles <2007S2913>. 

The regioselective coupling reaction of 2,3-dibromobenzo[/ ]furan with several terminal acetylenes was achieved using a palladium-catalyzed Sonogashira reaction, as exemplified in Equation (91) <2003S925>. 

CEt=CPh-0) are prepared from the regioselective coupling of the coordinated alkyne with an acetyl or benzoyl group in the reactions of Tp NbMe(OMe)(PhC=CR) and Tp NbPh(OMe)(PhC=CEt) with... 

Under similar conditions, reduction of an Qr,)6-unsaturated lactone linked to a linear a,)6-unsaturated ester gave modest yields of two isomeric spirolactones, [Eq. (17)]. CV of simple monofunctional compounds indicates that in this case the a,)6-unsaturated ester function is the electrophore [159]. The regioselective coupling ip to the ester group) and the presence of a proton donor (diethyl malonate) indicate that the probable reaction pathway is a-protonation of the radical anion, further reduction, and Michael addition of the resulting )6-anion to the lactone. 

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