Stilbene derivatives, modification

Stilbene derivatives can be reduced with alkali metals in liquid ammonia. The reaction is usually performed in a homogeneous medium to give substituted diphenylethane compounds as a mixture of enantiomeric forms. However, there are compounds (particularly, biologically active ones) for which the stereospecificity of synthesis has decisive importance. A simple modification of the reduction method with an alkali metal in liquid ammonia was found (Collins and Hobbs 1983), which makes it possible to perform the process stereoselectively. The metal is not predissolved, as is usual, but is added in small portions without trying to make the reaction medium homogeneous. Stereoselectivity is ensured by carrying out the reduction on the surface of the metal and not in the solution bulk. 

A series of new ( )-4,4 -bis(diphenylammo)stilbene derivatives have been synthesized to investigate nonlinear absorptivities with attention paid to the peripheral substituent effect and multibranched modification effect by the open aperture femtosecond Z-scan technique and the nanosecond nonlinear optical transmission (NET), respectively [36]. Two-photon fluorescence for ( )-4,4 -bis(di-phenylamino)stilbene in THE was detected. It was found that substituent group attached to the periphery of BDPAS has no obvious contribution to TPA enhancement and that the dramatic increase in effective TPA cross sections of multibranched samples in nanosecond regime strongly suggested their larger excited-state absorption. 

Stilbenoids are derived from cinnamic acid and three acetate units from mal-onyl coenzym A. The first part of the biosynthesis is in common to flavonoids. The two biosynthetic routes are diverging at the point of cyclization of a styryl-3,5,7-triketoheptanoic acid. A C-acylation produces a chalcone and subsequent modifications lead to the flavonoids. An aldol condensation of the same intermediate polyketide produces a stilbene-2-carboxylic acid that is unstable and constitutes a range of structures known as stilbenoids. Figure 9C.5 shows an overview of the biosynthetic pathway (Gorham 1995). 

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