Arylalkynes alkenylation

Terminal alkynes undergo the above-mentioned substitution reaction with aryl and alkenyl groups to form arylalkynes and enynes in the presence of Cul as described in Section 1.1.2.1. In addition, the insertion of terminal alkynes also takes place in the absence of Cul, and the alkenylpalladium complex 362 is formed as an intermediate, which cannot terminate by itself and must undergo further reactions such as alkene insertion or anion capture. These reactions of terminal alkynes are also treated in this section. 

Cross-coupling with Terminal Alkynes to Form Alkenyl- and Arylalkynes... 

The Pd-catalyzed cross-coupling of terminal alkynes with aryl and alkenyl halides in the presence of Cu(I) as co-catalyst to give arylalkynes and enynes is known as the Sonogashira coupling (first time reported by Kenkichi Sonogashira et ah). Triethylamine or diethylamine is used as a solvent. 

Intermolecular additions of alcohols to alkynes can be coupled with other tandem reactions of the alkenyl-gold intermediate. Thus, reaction between salicylaldehyde and phenylacetylenes can give access to the isoflavanone skeleton (equation 7), whereas a three-component addition of methylenecylopropylcarbinols, arylalkynes, and alcohols leads to bicyclic compounds (equation 8). ... 

The Pd-catalyzed reactions of alkynylzinc chlorides 22, which are readily obtainable in situ from anhydrous zinc chloride and alkynyllithium or -magnesium, with alkenyl iodides or bromides 21 provide the corresponding terminal or internal enynes 23 in high yield and with high (>97%) stereospecificity [Eq. (9)] [16]. Aryl bromides or iodides can also be used to produce arylalkynes [17]. 

As described above (Section 5.2), the Stephens-Castro reaction of alkynylcopper with aryl and vinyl halides in boiling pyridine is a useful route to aryl and vinyl acetylenes. Direct cross-coupling of organic halides, such as sp halides, with terminal alkynes is a more convenient procedure. Such a reaction is not so easy, but it can be done using a Pd-complex catalyst [41]. Especially facile Pd-catalyzed cross-coupling of aryl and alkenyl halides with terminal alkynes proceeds smoothly under mild conditions in the presence of a cocatalyst of cuprous iodide in amine solvents [Eq. (28)] [42]. This methodology is now used widely for the constiuction of conjugated arylalkyne or enyne systems [43], as described below. It is attractive from a synthetic point of view because mild reaction conditions and simplicity of the procedure are associated with recent developments in modem acetylene chemistry [44]. 

The Negishi palladium-catalyzed cross-coupling reaction of alkenyl, aryl, and alkynyl halides with unsaturated organozinc reagents provides a versatile method for preparing stereodefined arylalkenes, arylalkynes, conjugated dienes, and conjugated... 

Pd-catalyzed coupling reactions of terminal and internal alkynes 1 and 4 with halides are surveyed in this section. Reactions of alkynes with aryl and alkenyl halides are classified in to two types. The first one is the preparation of arylalkynes 2 and alkenylalkynes (1,3-enynes) 3 by the reactions of terminal alkynes 1 with aryl and alkenyl halides in the presence of Pd(0) and Cul as catalysts (section 3.4.2). The second one is insertion of internal alkynes 4 to aryl- and alkenylpalladium bonds formed by oxidative addition of halides, generating alkenylpalladiums 5, which are living species and undergo further transformations before termination. Terminal alkynes also undergo the insertion in the absence of Cul catalyst (section 3.4.3)... 

Direct introduction of sp carbon to alkynes by the reaction of Cu acetylides with aryl and alkenyl halides to form arylalkynes and alkenylalkynes is known as the Castro reaction [1]. Later it was found that coupling of terminal alkynes (1-alkynes) with halides proceeds more smoothly by using Pd catalysts. There are two methods of Pd-catalyzed coupling, hi 1975 direct coupling of 1-alkynes catalyzed by a phosphine-Pd(O) complex in the presence of amines was reported by Heck and Cassar as an extension of the Heck reaction to 1-alkynes [2,3]. In the same year, Sonogashira and Hagihara found that the addition of Cul as a co-catalyst gave better results, and the Pd(0)-CuI-catalyzed reaction is called the... 

Sonogashira reaction [4,5], A comprehensive review on Pd-catalyzed alkynylation was published recently by Negishi and Anastasia [6], Facile Pd(0)-CuI-catalyzed coupling of aryl and alkenyl halides with 1-alkynes is used extensively for the preparation of arylalkynes or enynes. 

He et al. described a PtCU-catalyzed intramolecular cyclization of o-isopropyl or o-benzyl arylalkynes 214, which yielded functionalized indenes 215 (Scheme 82) [69]. In contrast to a previous report [44], the terminal carbon of alkyne in this reaction was substituted with aryl substituent. Notably, (TuBr (2.0 equiv.) was indispensable to achieve high yield. Theoretically, platinum(II)-activated electrophilic alkyne initially abstracts a hydride from benzylic C-H in [1,4]-manner to generate a benzylic carbocation I, which subsequently intercepts nucleophilic alkenyl-platinum(II) to afford the 5-membered ring. 

Phosphonation. Mn(OAc)3 can promote direct phosphona-tion of arylalkenes. The method supports a wide range of substituents and usually results in acceptable yields (eq 39). The reaction conditions also enable direct phosphonation of arylalkynes. In this case, the intermediate alkenyl radical reacts with the adjacent aromatic ring to afford the corresponding l//-inden-l-one in good yield (eq 40). This method supports substitution on both aromatic rings. 

Z)-1,3-Enyne compounds were synthesized by palladium(ll)-acetate-catalysed direct dehydrogenative alkenylation of terminal arylalkynes with unactivated allylic ethers. Various terminal arylalkynes can participate in the reaction, stereoselec-tively affording the desired conjugated (Z)-l,3-enynes in moderate to good yield l,3-bis(diphenylphosphino)propane was used as a ligand. ... 

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