Diaryl alkynes

Alder/retrograde Diels-Alder reaction sequence of a diaryl alkyne with a 3,6-dicarbomethoxy tetrazine. The resulting diazine (14) is then reduced, cleaved and cyclized with Zn/acetic acid to the 2,3,4,5-tetrasubstituted pyrrole (15), which is then N-alkylated with a-bromo-4-methoxyacetophenone to give a pentasubstituted pyrrole (16). The synthesis of lukianol A is completed by ester hydrolysis, decarboxylation, ring closure and deprotection. 

Sonogashira coupling of alkyne 50 with aryl iodide 51 affords the diaryl alkyne 52 oxidation of which produces the 1,2-diketone 53. Hydrolysis of the acetal moiety prior to a proline-induced aldol cyclisation generates a chromanone from which the [ljbenzopyrano-[2,3-c][l]benzopyranone rotenoid system is obtained <07T11878>. 

A zirconium-silene complex was obtained during the course of our study on the synthesis of a zirconium-silyl complex. The zirconium-silene complex is formed from disilylzirconocene 2a, generated from Cp2ZrCl2 and 2 equivalents of Me2PhSiLi 8b. Zirconium-silene complex 3 should be in a state of equilibrium with zirconacyclopropane 3. The insertion of diaryl alkyne 14 or vinyl alkyne... 

One example of a bonafide bis(alkyne) complex has recently been prepared. Reaction of the in situ generated olefin complex prepared by alkylation of ( -CsHs ZrC 50 with the diaryl alkyne in Equation (7) yields 253.130 In this structure, C-C coupling has not occurred, presumably a result of the steric strain associated with the zirconacyclo-pentadienyl fragment (Equation (7)). The solid-state structure further establishes the compound as a bis(alkyne) complex. Computational studies suggest that a Zr(iv) resonance structure is the most suitable representation of the compound. However, reaction of 253 with iodine in THF yields ( -CsHs Zrle 254 and the dialkyne starting material, suggesting that the zirconium center can act as a source of Zr(n) (Equation (8)). 

Scheme 28. Cobalt catalyzed [2 + 2 + 2] cyclotrimerization of the diaryl alkyne (63) tothehexa-phenylbenzene (64) and modern Scholl-type reaction in the synthesis of hexabenzocoronene (62,[112])...

It is important to note that both aliphatic and aromatic vinyl ketones were viable substrates in which P-alkyl and P-aryl substitutions were tolerated. Diaryl alkynes, mono-aryl internal alkynes, nonaromatic internal alkynes, terminal alkynes, and free hydroxyl-bearing alkynes were all efficient participants. It should be mentioned that while ynoates were successful nucleophiles, enoate electrophiles were found to be poor participants in nickelotalyzed couplings. 

The fully unsaturated 1,3-oxazepine (45) (m.p. 161-162°C) was prepared in very low yield by electro-oxidation at a graphite plate electrode of the diaryl alkyne (44) in acetonitrile as solvent, the latter supplying the nitrogen and one carbon to the ring (Equation (3)). 

The anion of diazomethyltrimethylsilane, or, better, the more stable and easily prepared anions of the diethyl or dimethyl diazomethylphosphonates, condenses readily with carbonyl compounds to give the homologous alkynes [e.g. (137)->(138) (Scheme 35)]. The reaction also works well on preparing diaryl-alkynes but does not offer a route to mono- or di-alkylalkynes. 

Two Sonogashira coupling reactions can be used to make unsymmetrical diaryl alkynes by first using trimethylsilylacetylene. The trimethylsilyl protecting group can be removed by addition of fluoride (usually tetrabutylammonium fluoride, see Section 11.6). Show how such a sequence of reactions can be used to construct the following product when one reactant is phenyl iodide. 

A small amount of the diaryl alkyne product was obtained. The proposed catalytic cycle is shown in Scheme 1.40. It is believed that the silver carbonate is responsible for oxidizing the Pd(0) to Pd(II) in order to conclude the catalytic cycle. The Pd(0) species is presumed to be obtained via reductive elimination of the ditdkynylpcdladium(II) intermediate. 

Other syntheses using the Suzuki methodology include the preparation of carbon-ll-labeled palmitic acid with carbon-11 at the terminal position and a diaryl alkyne, glutamate-receptor agent, Figure 5.1. ... 

Scheme 3.20 Transformation of diaryl alkynes or traminal aUcynes to amides...

Jeffrey S. Moore of the University of Illinois prepared J. Org. Chem. 2008, 73, 4256) a Mo alkyne metathesis catalyst on fumed silica gel that converted 28 to 29 at room temperature. The cyclization was driven by the vacuum removal of 3-hex5me 30. In the same paper. Professor Moore used the insolubility of a product diaryl alkyne 31 to drive other cyclizations. 

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