Multi-component Cross-coupling Reactions

Furthermore, selected push-pull chromophores 84 were investigated by differential scanning calorimetry (DSC), revealing relatively low glass transition temperatures, Tg, a favorable property for composites in photorefractive materials [83], 

The concept of alkyne activation by Sonogashira coupling was successfully extended to the in situ generation of alkynones that are highly reactive and versatile synthetic equivalents of 1,3-dicarbonyl compounds. Interestingly, ynones can be readily synthesized in a catalytic fashion by Sonogashira coupling of an acyl chlor- 

Under the amine basic conditions, the subsequently added l-(2-oxoethyl)-pyridinium bromide derivatives 90 are transformed in situ into pyridinium ylides that undergo a [2 + 3] cycloaddition with the alkynone dipolarophiles present in the reaction mixture. The initial cycloadducts instantaneously aromatize to give rise to highly fluorescent indolizine derivatives 91. 

Fluorescence studies with pyridyl-substituted representatives revealed not only that indolizines and biindolizines are highly interesting fluorescence dyes but also that their fluorescence color can also be reversibly switched upon altering the pH of the medium. 

Since all novel furans 95 and pyrroles 98 exhibit a strong blue fluorescence with considerable Stokes shifts, where the absorption maxima are found in the range 7.max, abs = 312-327 nm and the emission occurs at 7,max at,s = 401-451 nm, this multi-component approach to fluorophores can be exploited for combinatorial optimization of emission properties. 

---

The cross-coupling reactions can be combined with catalytic cyclization of 2-alkynylphenols in a one-pot, multi-component coupling procedure leading to 2,3-disubstituted benzofurans 39 as shown in Scheme 25 . 

---