Cyclization-coupling reactions

A Pd(II)-catalyzed sequential cyclization-coupling reaction of allenyl N-tosylcar-bamates and acrolein has been developed (Scheme 16.97) [103]. The proposed mechanism involves intramolecular aminopalladation of an allene, followed by insertion of acrolein and carbon-Pd bond protonolysis. 

The palladium-catalyzed cyclizative coupling reaction of a-allenols 41 with alkenyl halides was also explored. The transformation of allenols 41 into spirocyclic disubstituted dihydrofuran (3-lactams 43 was readily achieved in high yields, by treatment with allyl bromide or 2,3-dibromopropene in the presence of palladium (II) chloride (5 mol%) (Scheme 14) [60]. 

On the basis of this palladium-mediated Michael addition cyclization process, a novel two-step synthetic entry into functionalized furan derivatives 67 has also been devised (Scheme 28). Substitution of benzylidene (or alkyli-dene) malonates for their ethoxymethylene analog (65) as activating olefins gave rise to the formation of the corresponding 2-ethoxy-4-arylidene tetrahy-drofurans 66. An in situ addition of potassium ferf-buloxidc induced a decar-boxylative elimination reaction which was followed by an isomerization of the exocyclic double bond. The entire process successively involved a conjugate addition, a palladium-catalyzed cyclization-coupling reaction, a base-induced eliminative decarboxylation, and finally, a double bond isomerization [73]. 

Pd-Catalyzed three-component cyclization-coupling reaction of methyl acetoacetate, propargyl bromide or carbonate and aryl halides gave tetrasubstituted furans with high regioselectivities and good yields <05JOC6980>. 

Scheme 152. C-C Bond Formation by (a) Heck Reaction, (b) Tandem Cyclization—Coupling Reaction, (c) Cross-Coupling Reaction with Organometallics, and (d) a-Arylation of Ketones and Amides...

Aurrecoechea and co-workers used a palladium(Il) catalyst to perform a palladium-catalyzed cyclization-coupling reaction to prepare... 

Baran et al. developed a radical cross-couphng reaction between arylboronic acids and trifluoroborates, in 2011 (Scheme 5.31) [56]. This methodology was applied to achieve a domino cyclization/coupling reaction. When the aryl boronic acid 144 was subjected to Ag+/S20g , a benzofuran radical was generated, which underwent a radical trap with 1,4-benzoquinone as the terminating radicophile. 

Diazo Coupling Reactions. Alkylphenols undergo a coupling reaction with dia2onium salts which is the basis for the preparation of a class of uv light stabilizers for polymers. The interaction of orxv i -nitrobenzenediazonium chloride with 2,4-di-/ r2 -butylphenol results in an azo-coupled product (30). Reduction of the nitro group followed by m situ cyclization affords the benzottiazole (31) (19). 

Tb allium (ITT) ttifluoroacetate promotes olefin cyclization reactions and intramolecular coupling reactions (32,33). 

The von Richter cinnoline process was further extended to solid-phase synthesis. The route began from benzylaminomethyl polystyrene and the required diverse o-haloaryl resins represented by 21 were prepared from substituted o-haloanilines. A Pd-mediated cross-coupling reaction with 21 and the alkynes provided the alkynylaryl derivatives represented by alkyne 22. The von Richter cyclization reaction with hydrobromic or hydrochloric acid in acetone/HaO and cleavage from the resin occurred in the same step to furnish the cinnoline derivatives 23 in 47-95% yield and 60-90% purity (no yield reported for each entry). 

Another synthetic application of an azo coupling reaction was found by Hecken-dorn (1987, 1990). In aqueous acetone a series of dialkyl (chloroacetamido)malo-nates, which are coupling components with a CH group activated by two carbonyl groups, were found to react with arenediazonium ions as in Scheme 12-44. The primary product cannot be isolated because it cyclizes easily to give a 1,2,4-triazin-5-one derivative (12.90). ... 

UV irradiation of heterocycles such as 53 in ethanol containing catalytic iodine leads to oxidative cyclization affording tosylphenanthrenoids 54 <96JOC1188>. The synthesis of a heterocycle related to 53 was accomplished by a titanium coupling reaction <96TL2721>. 

Uemura M (2004) (Arene)Cr(Co)3 Complexes Cyclization,Cycloaddition and Cross Coupling Reactions. 7 129-156 Ujaque G, see Drudis-Sole G (2005) 12 79-107... 

Nickel carbonyl effects coupling of allylic halides when the reaction is carried out in very polar solvents such as DMF or DMSO. This coupling reaction has been used intramolecularly to bring about cyclization of to-allylic halides and was found useful in the preparation of large rings. 

As described previously, the two-component coupling reaction between amidox-ime 50 and DM AD generated a mixture of Z- and E-adducts 51, which was heated in xylenes to afford hydroxypyrimidinone 55 (Scheme 6.20). The previously proposed mechanism involved tautomerization of 51 to 52, followed by a Claisen [3,3]-rearrangement to yield intermediate 53. Subsequent tautomerization of the intermediate 53 to 54, followed by cyclization would afford 55 [9a,f]. 

Organic halides play a fundamental role in organic chemistry. These compounds are important precursors for carbocations, carbanions, radicals, and carbenes and thus serve as an important platform for organic functional group transformations. Many classical reactions involve the reactions of organic halides. Examples of these reactions include the nucleophilic substitution reactions, elimination reactions, Grignard-type reactions, various transition-metal catalyzed coupling reactions, carbene-related cyclopropanations reactions, and radical cyclization reactions. All these reactions can be carried out in aqueous media. 

Metal complexes of lanthanides beyond lanthanocenes were used to catalyze the reductive coupling reaction of dienes. La[N(TMS)2h was found to effect the cyclization of 1,5-hexadiene in the presence of PhSiH3 (Eq. 13) [50]. Cyclized products 88 and 89 were isolated in a combined yield of 95% (88 89 = 4 1). It was suggested that the silacycloheptane 89 resulted from competitive alkene hydrosilylation followed by intramolecular hydrosilylation. 

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