Alkyne Migration in Alkylidene Carbenoid Species: A New Method of Polyyne Synthesis

Abstract

The synthesis of conjugated polyyne structures via a modification of the Fritsch-Buttenberg-Wiechell (FBW) rearrangement is reported. Our adaptation provides for the 1,2-migration of an alkyne in a carbene/carbenoid intermediate that is conveniently effected via lithium-halogen exchange with the appropriate dibromo-olefinic precursor. This rearrangement is quite rapidly accomplished under mild conditions (hexane solution, -78 degrees C), and the seemingly high migratory aptitude of the alkynyl moiety provides for efficient rearrangement. This, in turn, allows for multiple rearrangements in a single molecule, greatly facilitating the construction of highly unsaturated substrates. This procedure is exploited for the rapid synthesis of symmetrical and unsymmetrical 1,3,5-hexatriynes, extended polyynes, and aryl polyyne building blocks. Most significantly, many of these structures have been or would be difficult to access via more traditional transition metal catalyzed homo- or cross-coupling techniques.

Arrays of Molecular Rotors with Triptycene Stoppers: Surface Inclusion in Hexagonal Tris(o-phenylenedioxy)cyclotriphosphazene

“…36,37 At first, alkyne 10 was converted to ynone 32 in two steps (Scheme 7, route A). Lithiation of 10 followed by a reaction with paraformaldehyde resulted in alcohol 33, which was subsequently oxidized to ynone 32 by Swern oxidation.…”

A novel sulfonamide non-classical carbenoid: a mechanistic study for the synthesis of enediynes

“…Fortunately, Tykwinski et al have demonstrated that the migratory aptitude of alkynes in FWB rearrangements is poor in coordinating solvents. 23 We therefore concluded that any FWB rearrangement would most likely involve migration of the aryl group and we prepared three substrates to examine any putative rearrangements occurring. By altering the electron demand of the aryl substituent we hoped to gain some insight as to whether a 1,2-rearrangement was competing with enediyne formation.…”

Polyynes

“…Apart from dendrimer end-capped oligoynes, which mainly help to stabilize the system, many different functional end-groups have been incorporated into the two ends of sp carbon chains by chemists in order to study the electronic properties and explore possible applications of this class of compounds (Scheme 10.2) [10,[40][41][42][43]. The electronic structures of organic polyynyl chains with various end-groups have been studied by Bohlmann [35,36], Walton [44,45], Hirsch [12,13,39], and Tykwinski [46,47]. The electronic absorption spectra of the polyynes generally show highly structured absorption bands, with the lowest energy absorption bands showing a bathochromic shift with increasing number of CcC units.…”

“…In addition to the one-dimensional wire-like compounds, a considerable number of two-dimensional and three-dimensional architectures have also been built, using the chemistry of the alkynyl units in an elegant manner, by the groups of Bunz [54], Diederich [55][56][57], de Meijere [58], Moore [59], Tykwinski [46,47], Haley [60], Vollhardt [22][23][24][25][26][27] and others [61,62]. In particular, a series of perylene-terminated phenylene ethynylene dendrimers with energy gradients was successfully synthesized and isolated by Moore and coworkers (Scheme 10.5) [63]; the luminescence and energy transfer properties have been evaluated.…”