Amides intramolecular oxidative coupling

Finally, it has been found only recently that the intramolecular oxidative coupling of appropriately substituted monophenolic tetrahydrobenzyliso-quinolines induced by VOF3-TFA constitutes one of the simplest and most efficient routes to the aporphines. The only limitation here is that the nitrogen atom must be protected as the trifluoroacetyl amide or the borane complex, as illustrated by the two examples shown in Scheme 10.4. The yields are appreciably lower if the amine function is unprotected. ... 

The CuCl2-catalysed oxidative coupling of alkenes and aldehydes in presence of TBHP (t-butylhydroperoxide) is developed for the synthesis of unsaturated a,fi-ketones. Both the aldehydes and alkenes tolerated a variety of functional groups. A preliminary mechanistic study indicated that the reaction is likely to proceed through a single-electron transfer. A similar intramolecular oxidative coupling of substimted amides in the presence of t-BuONa affords corresponding oxindoles substituted in the... 

Intramolecular anodic coupling of diaryl amides is a synthetically interesting reaction that may be applied to the synthesis of alkaloidal structures [210]. However, this aryl coupling is initiated by the oxidation of an aromatic ring (aryl ether or phenol) and not by oxidation of the nitrogen. Therefore, it is not discussed further in this chapter. 

An interesting intramolecular version of such oxidative couplings was described by Hiyama et al. [18]. Starting from acyclic amides 38, deprotonation and oxidation with Cu(OAc)2 generates diradicals, which undergo cyclization to synthetically useful j9-lactams 39 (Scheme 13). However, the reactions proceed with only moderate yield and stereoselectivity. 

A similar ruthenacyclopentene intermediate can be proposed for the coupling of alkynes and allylic alcohols to lead to Y,8-unsaturated aldehydes and ketones. When [Cp Ru(CH3CN)3]PFg was used as a catalyst, the catalytic coupling between propargylic amides and allylic alcohols selectively provided piperidine derivatives by cyclization of the highly reactive aminoaldehyde intermediate [65] [Eq. (27)]. Only the branched isomer was formed by oxidative coupling, allowing the intramolecular condensation. 

Finally, the intramolecular coupling reaction between an olefin and a pyrrole ring has been examined (Scheme 40). In this example, a 66% isolated yield of the six-membered ring product was obtained. A vinyl sulfide moiety was used as the olefin participant and the nitrogen protected as the pivaloyl amide in order to minimize the competition between substrate and product oxidation. Unlike the furan cyclizations, the anodic oxidation of the pyrrole-based substrate led mainly to the desired aromatic product without the need for subsequent treatment with acid. 

A number of related couplings have been reported during the synthesis of the alkaloid ( )-cryptopleurine149 and also intramolecular coupling of diaryl amides to dibenzazepine and dibenzazodne structures.150 A versatile method for the preparation of tetrahydroquinolines and jololidines has been developed.151 The method involves the anodic oxidation of AT,AT-dimethyl-aniline in methanol to afford a-methoxylated or a, a -dimethoxylated compounds and subsequent treatment of products with Lewis acids in the presence of olefins. 

Otherwise, lithium amides of secondary amines undergo anodic dimerization to form hydrazines in moderate yields [12]. Hydrazines are also generated, if secondary amines are electrochemically oxidized in the presence of an alkali hydroxide [27,28]. This reaction is mainly effective if the coupling takes place intramolecularly to give cyclic hydrazine derivatives [28]. If lithium amides of secondary amines are anodically oxidized in tetrahydro-furan (THF) solution in the presence of the free amine, 2-aminotetrahydrofurans are formed in reasonable yields. In contrast, the respective aminomagnesium bromides only gives A, A -coupling products [29]. 

Secondary phosphine oxides were used as ligands/preligands in palladium catalysts that were useful in the Suzuki-Miyaura coupling, in intramolecular ot-arylations of amides and in the arylation of indoles. ... 

In this domino process, benzylamine was reacted with 2-halobenzamides through UUman-type coupling to yield the N-arylated intermediate 144 (Scheme 9.26). Then, a copper-catalyzed aerobic oxidation of 144 afforded the intermediate 145, which underwent an intramolecular nucleophilic addition of the amide to provide 146. Under the used reaction conditions, the intermediate 146 was oxidized to provide the desired products 147 in excellent yield. This protocol was also utilized by Fu et al. [80] by employing easily available a-amino adds instead of benzylamines to synthesize similar analogs. Very recently, the same method was applied for the synthesis of pyrimido[4,5-b]carbazoles by Nagarajan et al. [81]. 

Rhodium(lll)-catalyzed redox—neutral coupling of N-phenoxyacet-amides and alkynes led to benzo[l)]furan derivatives (13AGE6033). Furo[2,3-l)]pyran-6-one derivatives were prepared via rhodium(II)-catalyzed reactions of diazo compounds and ethynyl compounds (13T9294). Copper-mediated oxidative annulation of phenols and unactivated internal alkynes afforded benzo[l ]furan derivatives (13CS3706). E t-kaurane maoecrystalV was produced via C-H functionalization (13JA14552). Rhodium-catalyzed intramolecular C-H... 

Sainsbury M, Wyatt J (1976) Intramolecular coupling of diaryl amides by anodic oxidation. J Chem Soc Perkin Trans 1 661-664... 

Intramolecular C( p )-N coupling between the benzylic C anion and nitrogen-based anions in THF yields various azacycles through oxidation of the dianions with iodine in the presence of -BuLi and ZnCl2 as the additive. The optimal reaction conditions for C(ip )-N coupling are readily applicable to less acidic substrates, conformationally unbiased substrates to form six- and seven-membered azacycles and amide substrates that give rise to less-reactive nitrogen nucleophiles." ... 

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