Diynes coupling

Hence this chapter provides analogy between silylene and carbene chemistry as a useful approach for construction of small-ring monosilacycles. Furthermore, intramolecular Wurtz, Diyne coupling, Kipping and Gilman reactions have been shown to be useful tools for construction of medium-ring oligosilacycles. 

IV. RING FORMATION BY WURTZ AND DIYNE COUPLING REACTIONS A. Heptasila[7]paracyclophane... 

General Procedure for 1,3-Diyne Coupling with Aryl Iodides... 

The terminal diyne 320 is prepared by coupling of the zinc acetylide 318 with /rfln.s-l-iodo-2-chloroethylenc (319), followed by elimination of HCI with sodium amide[231]. Similarly, terminal di- and triynes are prepared by using cw-l,2-dichloroethylene[232]. The 1-alkenyl or l-aryl-2-(perefluoroalkyl) acetylene 321 is prepared by the reaction of a zinc acetylide with halides[233]. 

The alkynyl iodide 359 undergoes cross-coupling with a terminal alkyne to give the 1,3-diyne 360[264]. No homocoupling product is formed. This reaction offers a good synthetic method for unsymmetrical 1,3-diynes. 

The synthesis can be conducted both in solution and without solvents. The reaction in solvent (e.g., methanol, ethanol, dioxane, dimethylformamide) is recommended for volatile 1,3-diynes and amines in this case the pyrroles are purer and the yield is higher. With disubstituted diacetylenes, ammonia and primary alkyl- and arylamines produce 1,2,3-trisubstituted pyrroles under the same conditions (65CB98 71MI1). Since disubstituted diacetylenes are readily obtained by oxidative coupling of acetylenes (98MI2), this reaction provides a preparative route to a wide range of pyrroles. 

With the exocyclic alkylidene at C-13 properly in place, the elaboration of the l,5-diyn-3-ene moiety can now be addressed. Cleavage of both acetate and trimethylsilyl functions in 86 with basic methanol, followed by triethylsilylation of the newly formed tertiary hydroxyl group, efficiently affords alkyne 25 (86 % overall yield). This substance was regarded as a viable candidate for a Pd-catalyzed coupling reaction.12 Indeed, treatment of 25 with (Z)-chloroenyne 26 in the presence of a catalytic amount of Pd(PPh3)4 and Cu1 results in the formation of enediyne 24 in 91 % yield. 

Haloalkynes (R—C=C—X) react with ArSnBu3 and Cul to give R—C= C—Ar. Acetylene reacts with two equivalents of iodobenzene, in the presence of a palladium catalyst and Cul, to give 1,2-diphenylethyne. 1-Trialkylsilyl alkynes react with 1-haloalkynes, in the presence of a CuCl catalyst, to give diynes and with aryl triflates to give 1-aryl alkynes. Alkynes couple with alkyl halides in the presence of Sml2/Sm. Alkynes react with hypervalent iodine compounds " and with reactive alkanes such as adamantane in the presence of AIBN. ... 

Terminal alkynes can be coupled by heating with stoichiometric amounts of cupric salts in pyridine or a similar base. This reaction, which produces symmetrical diynes... 

The subsequent chain extension can be accomplished by the pedestrian step-by-step homologation sequence via the acyclic diyne 12 or by a more efficient block-to-block strategy. The step-by-step approach includes protiodesilylation of diyne 12 followed by coupling with the propargyl chloride 9 following the same protocol as for the preparation of 12 from 11 and subsequent repetitions of protiodesilylation and alkylation with chloride 9 to reach stages 16 and 18, respectively (Scheme 3). 

The oxidative coupling, however, normally provides better results, as was demonstrated by the reasonably efficient cyclization of 179 to the homoconjugated 16-membered macrocycle 180 (14% yield) with alternating ethyne and butadiyne units (Scheme 34) the alternative Cadiot-Chodkiewicz coupling of the bisterminal diyne 38 and the dibromotriyne 177 gave only a 2.6% yield of 180 [4]. 

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