An expedient synthesis of N,N-dialkylamino-dihydroxanthene-pyrylium conjugated near-infrared fluorescent dyes

摘要

An expedient synthesis of amino-(nor)dihydroxanthene-based fluorophores is reported, proceeding in two steps from commercially available salicylic aldehydes. The synthesis relies on the one-pot construction of the (nor)dihydroxanthene scaffolds through an oxa-Michael/retro-Michael/vinylogous aldol/dehydration cascade sequence. Further extension of the pi-conjugated systems through a condensation reaction with a 2,4,6-trisubstituted pyrylium salt led to a novel class of near-infrared (NIR) fluorescent dyes with absorption/emission maxima in polar media in the ranges of 705-778 and 785-828 nm, respectively. (C) 2015 Elsevier Ltd. All rights reserved.