The first efficient method for the intramolecular trapping of benzynes by phenols: a new approach to xanthenes

Abstract

Condensations between the dianion 1 derived from 1-(N-butoxycarbonylamino)-1H-benzotriazole and silyloxysalicylaldehydes 10 give excellent yields of the expected adducts 11. While attempts to remove the N-Boc function were unsuccessful, desilylation and hydrogenolysis delivered the hydroxybenzyl derivative 14 which could be efficiently deprotected to give the amine 15. This then underwent smooth decomposition to the benzyne 16, upon exposure to N-iodosuccinimide, and intramolecular trapping by the phenol group, with incorporation of iodine, to give the iodoxanthene 17. A more efficient protocol featured condensation of dianion 1 with 2-(benzyloxy)aryl aldehydes; hydrogenolysis of the initial products 19 and 22a served both to deprotect the phenol function and to effect hydrogenolysis of the benzylic alcohol group. A final acidic deprotection and exposure to N-iodosuccinimide delivered good yields of the iodoxanthenes 21 and 23, demonstrating for the first time a viable method for the intramolecular trapping of benzynes by phenolic groups.

Silica supported perchloric acid: an efficient catalyst for the synthesis of 14-aryl-14H-dibenzo[a,i]xanthene-8,13-diones

“…5 The other useful applications of this heterocycles are as dyes, 6 fluorescent materials for visualization of biomolecules, 7 and in laser technologies. 8 Many procedures have been developed for the synthesis of xanthenes and benzoxanthenes, which include trapping of benzynes by phenols, 9 cyclocondensation between 2-hydroxyaromatic aldehydes and 2-tetralone, 10 cyclodehydrations, 11 and intramolecular phenyl carbonyl reaction of aldehydes with 5,5-dimethylcyclohexane-1,3-dione 12 or β-naphthol. 13 Furthermore, the synthesis of benzoxanthenes and their related products include the reaction of β-naphthol with formamide, 14 carbon monoxide, 15 2-naphthol-1-methanol, 16 aldehydes and cyclic 1,3-dicarbonyl compounds.…”

Benzotriazole-Mediated Synthesis of Oxygen-Containing Heterocycles

“…The corresponding benzyne derivative underwent an intramolecular cyclization to give the iodoxanthenes 147 in excellent overall yields. This work demonstrated for the first time a viable method for the intramolecular trapping of benzyne derivatives by phenolic groups (Scheme 30) [50,51].…”

Oxidative cyclization in the synthesis of 5‐ and 6‐membered N,O‐heterocycles

“…I 2 has been used for the intramolecular trapping of benzynes 382 by a suitably situated phenol group (Scheme 89) [195].…”