An efficient synthesis of novel 11H-chromeno[3',2':3,4]pyrrolo-[2,1-b][1,3]thiazol-11-one heterocyclic system

Nucleophile-induced ring contraction in pyrrolo[2,1-c][1,4]benzothiazines: access to pyrrolo[2,1-b][1,3]benzothiazoles

“…The first group of approaches to the PBTA scaffold is an annulation of benzothiazoles with a pyrrole moiety ( Scheme 1 ). It includes intramolecular cyclizations of benzothiazoles bearing a 3'-chloro substituent at C 2 position ( Scheme 1 , entries 1 and 2) [ 5 – 7 ], intramolecular catalytic carbene cascade reactions of propargyl 1,3-benzothiazol-2-yl(diazo)acetates ( Scheme 1 , entry 3) [ 12 ], dearomative [3 + 2] cycloaddition reactions of benzothiazoles with cyclopropanes ( Scheme 1 , entry 4) [ 13 – 15 ], multicomponent reactions (MCRs) of benzothiazoles, isocyanides and 2-methylidenemalonates ( Scheme 1 , entry 5) [ 16 ], 1,3-dipolar cycloadditions of N -alkylbenzothiazolium salts ( Scheme 1 , entry 6) [ 17 – 22 ], MCRs of 2-methylbenzothiazole, acetylenedicarboxylates and active methylene compounds ( Scheme 1 , entry 7) [ 23 – 25 ], MCRs of (1,3-benzothiazol-2-yl)acetonitrile, aldehydes and acylcyanides ( Scheme 1 , enry 8) [ 3 , 26 ] and reactions of 3-acyl-2,3-dihydro-1,3-benzothiazole-2-carbonitriles with acetylenedicarboxylate ( Scheme 1 , entry 9) [ 4 ].…”