Phase transfer catalysis crosslinking

A crosslinked rubber particle can be considered as a viscous hydrocarbon phase. In principle, phase transfer catalysis should apply to the chemistry of inorganic ions within such particles,... 

A series of 3-alkyl- and 3-aryl-7/7-furo[3,2- ]-l-benzopyran-7-ones 78 (linear furocoumarins) was synthesized and evaluated for their photochemical and nonphotochemical crosslink formation with DNA as well as for their spectro-photometric and fluorescent properties, lipophilicity, and ability to photobleach A, A -dimethyl-/)-nitrosoaniline (RNO) after irradiation with UVA light <2002AP187>. The synthesis of the linear furocoumarins (Scheme 10) was a modification of a previously published method in which 7-hydroxy-2//-l-benzopyran-2-ones 76 were converted into / -ketoethers 77 by alkylation with haloketones under phase-transfer catalysis conditions. Base-catalyzed intramolecular condensation and subsequent acidification gave the corresponding 78. A molecular complex between each one of these fluorescent furocoumarins and DNA was observed, but only compounds with a 3-Me or 3-Ph group showed UVA irradiation-induced crosslink formation. 

Nichols, P.P. The scission of polysulfide crosslinks in scrap rubber particles through phase transfer catalysis. Rubber Chem. Technol. 1982, 55, 1499. 

The asymmetric alkylation of glycine derivatives is one of the most simple methods by which to obtain optically active a-amino acids [31]. The enantioselective alkylation of glycine Schiff base 52 under phase-transfer catalysis (PTC) conditions and catalyzed by a quaternary cinchona alkaloid, as pioneered by O Donnell [32], allowed impressive degrees of enantioselection to be achieved using only a very simple procedure. Some examples of polymer-supported cinchona alkaloids are shown in Scheme 3.14. Polymer-supported chiral quaternary ammonium salts 48 have been easily prepared from crosslinked chloromethylated polystyrene (Merrifield resin) with an excess of cinchona alkaloid in refluxing toluene [33]. The use of these polymer-supported quaternary ammonium salts allowed high enantioselectivities (up to 90% ee) to be obtained. 

In fact, we have successfully used phase transfer catalysis to reduce the occurrence of site-site interactions (which cause additional crosslinking) in the reaction of pol3nner I with 1,4-butanedithiol in the presence of base according to Scheme 2 (Ref. 14). 

Free 1979a Frechet, J.M.J., de Smet, M. and Farrall, M.J., Chemical Modification of Crosslinked Resins by Phase Transfer Catalysis Preparation of Polymer-Bound Dinitriles and Diamines, Tetrahedron Lett., (1979) 137-138. 

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