Cyclization, reductive substitution reaction

Tandem cyclization/3-substitution can be achieved starting with o-(trifluoro-acetamido)phenylacetylenes. Cyclization and coupling with cycloalkenyl trif-lates can be done with Pd(PPh3)4 as the catalyst[9]. The Pd presumably cycles between the (0) and (II) oxidation levels by oxidative addition with the triflate and the reductive elimination which completes the 3-alkenylation. The N-protecting group is removed by solvolysis under the reaction conditions, 3-Aryl groups can also be introduced using aryl iodides[9]. 

Furthermore, the copper-mediated SN2 substitution reaction is not restricted to carbon-carbon bond formation, as can be seen form the synthesis of silylallenes [15], stannylallenes [16] and bromoallenes [17] using propargylic electrophiles and the corresponding heterocuprates. The resulting allenes are often used as intermediates in target-oriented synthesis, e.g. in cyclization and reduction reactions [15-17]. 

Few examples of photochemical dehydrogenation reactions accompanied by cyclization are reported in the literature. 2,3,5-Triphenyl-tetrazolium chloride (CV), which is used biochemically as reduction indicator, on irradiation in ethanol with ultraviolet light, undergoes dehydrogenation accompanied by cyclization to yield 2,3 (2,2 -bi-phenylene)-5-phenyltetrazolium chloride (CVI).106 167 Light-induced cyclization of substituted derivatives of CV to the corresponding bi-phenylene derivatives has been reported recently. sl 33... 

A tandem radical 5-exo cyclization/radical addition/allylic substitution reaction was subsequently described [292]. Allylic ot-bromo acetal 242b cyclized cobalt-catalyzed. Addition to diene 245 and subsequent coupling with coformed organocobalt(I) species generates an allylcobalt complex, which undergoes reductive elimination to cyclic product 246 in 93% yield (cf. Fig. 56). 

Bixchler Napiralski, Dieckmann cyclization [15], Suzuki reaction [48], Wittig reaction, ozonolysis, condensation, esterification, nucleophilic substitution [49], Henry reaction, 1.3-dipolar cyclo-addition, electrophilic addition [50], oxidation chloride -> aldehyde [50], sulfide —> sulfone [51], alcohol —> ketone, Arbuzov reaction (phosphine-phosphorox-ide) [52], reduction hydration [45], ester -> alcohol [49, 53]... 

No new TV-benzyltetrahydroisoquinolines have been isolated from natural sources in recent years. However, the structure of corgoine has been confirmed by three syntheses. The first involves reduction of the 7V-benzyl quaternary salt derived from isoquinoline 1, whereas the second approach utilizes the Pictet-Spengler reaction to cyclize the substituted phenethylamine 2 (see Scheme 31.1). The third synthesis of corgoine involves heating 6-methoxy-7-hydroxy-tetrahydroisoquinoline with / -hydroxybenzyl alcohol to afford the alkaloid in 44% yield. The A -benzylation probably occurs through the intermediacy of /7-benzoquinone methide which adds to the basic nitrogen of the isoquinoline. ... 

Olefin migration Oxidation of alcohols Passerini reaction Pauson-Khand reaction Pinacol cross-coupling Pinner reaction Polymerization of olefins Prins reaction Propargylation Radical addition Radical cyclization Radical substitution Reduction... 

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