Polyynes Via Alkylidene Carbenes and Carbenoids

Abstract

of detail it also surveys some of the unique properties displayed by these newly obtained materials, including solid-state structure and stability, and the linear and nonlinear optical properties of conjugated polyynes. Alkylidene Carbene and Carbenoid SpeciesAlkylidene carbenes/carbenoids (1 and 2) are reactive intermediates capable of undergoing several distinct reactions (Scheme 7.1) [13]. Carbenoid 1 and alkylidene carbene 2 are distinguished by the association of the carbon in 1 with a metal and a halogen (or another leaving group), while the free carbene 2 has no such ties. The two extremes can vary greatly in reactivity. Within this range of reactivity, solvent, b-substituent, and temperature can all affect the reaction outcome. For carbenoid intermediates, both the metal and the leaving group can also greatly influence the reaction [13e]. 261 7.3 Alkyne Formation from Carbenes and Carbenoids R R' 17 70% 16a X = ZnX 16b X = Li -20 ˚C to rt Et 2 O Equation 7-1 263 7.3 Alkyne Formation from Carbenes and Carbenoids H Cl BuLi, THF -90 ˚C 18 19 77% Equation 7-2 CH 3 H Cl CH 3 BuLi THF/Et 2 O > -70 ˚C 20 21 65% Equation 7-3 H Br Br Br t-BuOK ∆ 23 24 22 -40 ˚C to 0 ˚C PhLi, benzene/ether Equation 7-4 265 7.3 Alkyne Formation from Carbenes and Carbenoids Cl Cl Cl S Cl S S S S S S S BuLi, THF -90 to 0 ˚C 31 32 30% Equation 7-6 a Dibromoolefin formation as in Scheme 7.5.

Oligomers from sp-Hybridized Carbon: Cumulenes and Polyynes

“…The formation of polyynes series [79], and Ph F [n] [80,81] has been accomplished via FBW rearrangement, using several variations on a common theme that typically targets dibromoolefins as stable and readily available precursors to polyynes [12,[82][83][84]. Two examples have been outlined in Scheme 9.…”