Chemoselective coupling reaction

This method of imidazolylzinc chloride synthesis has also found application in the synthesis of a sulfonyl chloride to be used in the preparation of some potential factor Xa inhibitors [17]. Thus, following imidazole metalation and quenching with ZnCl2, a chemoselective coupling reaction occurred to provide 16. Treatment with sulfur dioxide provided the sulfinic acid, which upon treatment with thionyl chloride, provided the requisite sulfonyl chloride 17. 

Coupling reactions. Sequential and chemoselective coupling reactions have been developed for 3-chloro-4-arylthio-l,2-cyclobutenones. Thus a Stille coupling replaces the chlorine atom with a Suzuki coupling to follow. Two different Pd complexes are used. ... 

Mn. Manganese is also effective for mediating aqueous carbonyl ally-lations and pinacol-coupling reactions. Manganese offers a higher reactivity and complete chemoselectivity toward allylation of aromatic aldehydes.178... 

The research has inspired related investigation into the coupling reaction between aromatic aldehydes and benzyl bromide or chloride in water. The yields are slightly higher than the results for allylation despite the fact that aqueous benzylation is intrinsically more difficult than allylation. It is also found that the coupling reaction is chemoselective for aromatic aldehydes over aliphatic aldehydes, and also for aromatic aldehydes over aromatic ketones.98 Aqueous Grignard chemistry is attractive for its use of an environmentally benign solvent, and has been the subject of several... 

In addition, the reaction is very chemoselective and even a keto group is tolerated (Table 5). It should be underlined that this procedure compares advantageously to the corresponding palladium- or nickel-catalyzed coupling reactions. 

The thermodynamic driving force notwithstanding, the coupling of two different radicals is not an especially practical preparative method to form a new bond. This is because the preparation of precursors that directly decompose to radicals is rarely convenient, because disproportionation can often compete effectively with recombination, and especially because chemoselectivity (that is, the selective-coupling of two different radicals to the exclusion of self-coupling) is difficult to achieve if all coupling reactions occur at the same rate (the diffusion-controlled limit). 

Furthermore, bromothioethenes were reported as fairly useful electrophiles for the coupling reaction with secondary Grignard reagents (Table 5.1, entries 18 and 19) [13]. These transformations occur highly stereo- and chemoselectively at the vinyl bromide moiety whereas the thiophene functionality remains conserved under the described reaction conditions. 

Scheme 5.13 Chemoselectivity profile in iron-catalyzed cross-coupling reactions.

The reaction of chromenes with mono- and bis- imides of 1,4-benzoquinones (6, X = O or NCOPh) is promoted by Lewis acids and affords pterocarpans and azapterocarpans, respectively (95TL2713). A total synthesis of the pterocarpan, neorautenane, involves a chemoselective coupling of a benzodipyran with o-chloro-mercuriophenol (95JCS(P1)949). 

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