Double elimination protocol for access to unsymmetrically substituted aromatic polyynes starting from sulfones and aldehydes

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

Generation and trapping of a cage annulated vinylidenecarbene and approaches to its cycloalkyne isomer

A novel cage-annulated (bis-homocubyl) vinylidenecarbene has been generated and successfully trapped without any intermediacy of its cycloalkyne isomer. The greater kinetic and thermodynamic stability of the vinylidenecarbene vis-à-vis its cycloalkyne isomer has been predicted by DFT B3LYP/6-31G* calculations. The calculated results suggest the prospects of the cycloalkyne becoming amenable for trapping, if generated under suitable experimental conditions, owing to the substantial kinetic energy barrier associated with its possible ring contraction via 1,2-shift to the vinylidenecarbene isomer and marginal ground state energy difference. However, all of our attempts to directly generate and trap the cycloalkyne yielded unsatisfactory results. Attempted generation and trapping of a C2-symmetric bis-vinylidenecarbene from a bis-vinylidenedibromide met with unexpected failure.

Development of an oxazole conjunctive reagent and application to the total synthesis of siphonazoles

The preparation of 4-carbethoxy-5-methyl-2-(phenylsulfonyl)methyloxazole and its use in the elaboration of more complex oxazoles are described. A total synthesis of the unique natural products siphonazoles A and B, illustrates an application of this building block. A discussion of the biological activity of the siphonazoles is also presented.

A Facile Stereoselective Synthesis of (Z)-2-ethoxycarbonyl-substituted 1,3-enynes from (E)-α-stannyl-α,β-unsaturated esters and alkynyl bromides

Palladium-catalysed hydrostannylation of alkynyl esters in benzene at room temperature gives regio- and stereoselectively ( E)-α-stannyl-α,β-unsaturated esters in good yields. ( E)-α-Stannyl-α,β-unsaturated ethyl esters are difunctional group reagents which undergo Stille coupling reactions with alkynyl bromides in the presence of Pd(PPh3)4 and Cul co-catalyst to afford stereoselectively ( Z)-2-ethoxycarbonyl-substituted 1,3-enynes in good yields.

Synthesis and Spectroscopic Studies of Arylethynylsilanes

A variety of arylethynylsilanes (Ar-C[triple bond]C-C6H4-C[triple bond]C)(n)SiMe(4-n) were prepared successfully by reaction of the corresponding chlorosilanes Me(4-n)SiCl(n) with Ar-C[triple bond]C-C6H4-C[triple bond]CM (M = Li, MgBr), which was prepared by treatment of ethynyl(diarylethyne)s Ar-C[triple bond]C-C6H4-C[triple bond]CH with BuLi or MeMgBr. The ethynyl(diarylethyne)s were readily prepared in good yields by the double-elimination method: addition of lithium hexamethyldisilazide to a mixture of ArCH2SO2Ph, TMS-C[triple bond]C-C6H4-CHO, and ClP(O)(OEt)2, followed by desilylation. In the tetrakis(arylethynyl)silanes (Ar-C[triple bond]C-C6H4-C[triple bond]C)4Si thus prepared, through-space conjugation of four triple bonds on the silicon atom emerges as a result of participation of the silicon orbitals in the acetylenic pi orbitals. This participation enhances the emissive quantum yields of arylethynylsilanes with an increase in the number of arylethynyl moieties on silicon: quantum yields of emission (phiF) of 0.72 for (MeOC6H4-C[triple bond]C-C6H4-C[triple bond]C)4Si, 0.53 for (MeOC6H4-C[triple bond]C-C6H4-C[triple bond]C)2SiMe2, and 0.47 for MeO-C6H4-C[triple bond]C-C6H4-C[triple bond]CSiMe3 were obtained. Although this enhancement effect was also observed in the phenylethynylarylsilane (MeOC6H4-C[triple bond]C-C6H4)2SiMe2, the bis(arylethynyl)disilane (MeOC6H4-C[triple bond]C-C6H4-C[triple bond]C-SiMe2)2 exhibited non-enhanced emission.

One-Shot Double Elimination Process: A Practical and Concise Protocol for Diaryl Acetylenes

A variety of diaryl acetylenes were obtained in good yields when lithium hexamethyldisilazide was added to a solution of arylmethyl sulfone, aryl aldehyde, and chlorodiethylphosphate in THF. In this one-shot process, a number of transformations such as aldol reaction, phosphorylation of aldolate, and double elimination of the resulting beta-substituted sulfone proceeded successively to afford the desired acetylenes. The one-shot process was accelerated by the substitution of halogen atoms on the phenyl groups, and unsymmetrically substituted diaryl acetylenes were obtained without contamination of the dehalogenated products. Diaryl acetylenes with other substituents such as CF3, ethoxycarbonyl, dimethylamino, TMS-acetylene groups, as well as pyridinyl and thienyl moieties were also accessible with this method. However, methoxy-substituted compounds were obtained in moderate yields under the same conditions, but the yields were increased when lithium diisopropylamide was used instead.

Novel Synthesis of 2-Aryl and 2,3-Disubstituted Indoles by Modified Double Elimination Protocol

[reaction: see text] Syntheses of 2-aryl and 2,3-substituted indoles were realized by modified double elimination protocol. Under basic conditions, vinyl sulfones derived from the reaction of 2-aminobenzyl sulfone with benzaldehydes underwent cyclization and alkylation followed by elimination of sulfinic acid to afford 2,3-substituted indoles.