Protonation and alkylation of cross-conjugated ω,ω’-bis(dimethylamino) ketones (ketocyanines) containing the piperidine ring and the synthesis of the corresponding thiapentacarbocyanine dyes

Abstract

Protonation and alkylation of cross conjugated ω ω ω ω ω,ω ω ω ω ω´ bis(dimethylamino) ketones (ketocyanines) containing the piperidine ring and the synthesis of the corresponding thiapentacarbocyanine dyes Protonation or alkylation of 3,5 bis(3 dimethylaminoprop 2 enylidene) 1 methylpiperi din 4 one with Et 2 O•HBF 4 , Et 3 O + BF 4 -, Me 2 SO 4 , or Et 2 SO 4 (1 equiv.) involves the endocy clic N atom, yielding the corresponding piperidinium salts. With 2 equivalents of the above reagents, the reactions occur at two reactive sites (the N and O atoms) to give doubly charged 4 hydroxy or 4 alkoxy polymethine salts. Protonation and alkylation of ethyl 3,5 bis(3 dimethyl aminoprop 2 enylidene) 4 oxopiperidine 1 carboxylate involve only the O atom, affording the corresponding singly charged 4 hydroxy and 4 alkoxy polymethine salts. The latter were used to obtain previously unknown meso alkoxythiapentacarbocyanine dyes containing the 1 ethoxycarbonyl 1,2,3,6 tetrahydropyridine fragment in the polymethine chain.