Nucleophilic coupling

Alternatively, copper salts can themselves be engaged in transmetalation with a nucleophilic coupling partner to give organocopper intermediates, which then either enter the Pd-catalyzed... 

As described above, our synthetic strategy involves the convergent construction of the central cyclopentanone ring with a carbonylative cross-coupling reaction and a photo-Nazarov cyclization reaction (Chart 2.2). The electrophilic coupling component 51 was synthesized by an intramolecular Diels-Alder reaction [34] and the nucleophilic coupling component 52 by a vinyiogous Mukaiyama aldol reaction [35]. 

The synthesis of the nucleophilic coupling component 52 started with the reduction of 3-bromo-2-methylbenzenecarboxylic acid, and followed with a Homer-Wads worth-Emmons reaction of the corresponding aldehyde, and a 1,2-reduction of... 

Many other substrate-nucleophile couples have been similarly investigated in liquid ammonia and found to conform to the Sr I mechanism quantitatively. Among them, several systems give rise to unusual cyclic voltammetry patterns, exhibiting dips between the two waves of the starting halide (Pinson and Saveant, 1978) or trace crossing upon scan reversal (Amatore et al., 1980a). Examples of such behaviour are shown in Fig. 16. 

Stetter expanded Umpolung reactivity to include the addition of acyl anion equivalents to a,P-unsaturated acceptors to afford 1,4-dicarbonyls Eq. 5a [57-60]. Utilizing cyanide or thiazolylidene carbenes as catalysts, Stetter showed that a variety of aromatic and aliphatic aldehydes act as competent nucleophilic coupling partners with a wide range of a,p-unsaturated ketones, esters, and nitriles [61]. The ability to bring two different electrophilic partners... 

Dehydroheteroarenes like (10) and (11) have also been proposed as intermediates in nucleophilic substitution.23-25 Some of these reactions were evaluated uncritically and operation of other mechanisms like addition-elimination (AE) and ring opening-ring closure (ANRORC) can now be demonstrated in many such cases. Nevertheless, there is conclusive evidence for heteroaryne intermediacy in some reactions of heterocyclic halides. From the preparative point of view, nucleophilic coupling of such intermediates has found only limited applications.26-28 Reactive intermediates with an additional formal bond between nonadjacent atoms, like (12) and (13), have also been postulated but again hold little synthetic interest. 

Arynic substitution is a versatile technique of functional group transformation in aromatic systems and has found varied applications in preparation of simple compounds and in multi-step synthesis.3 4,3 The present section comprises examples illustrative of its synthetic scope. Attention is also drawn to some allied strategies which, when used in conjunction with the nucleophilic coupling of arynes, have opened convenient routes to complex natural products. 

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