Premium
Ring Expansion vs. Cleavage of the Exocyclic Double Bond of 2‐Cycloalkylidenedihydrobenzothiazoles and ‐benzimidazoles by Methanesulfonyl Azide
Author(s) -
Quast Helmut,
Ivanova Svetlana
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200004)2000:7<1229::aid-ejoc1229>3.0.co;2-n
Subject(s) - chemistry , deprotonation , zwitterion , sodium hydride , hydride , azide , ring (chemistry) , medicinal chemistry , bond cleavage , stereochemistry , yield (engineering) , cleavage (geology) , sodium azide , double bond , molecule , polymer chemistry , organic chemistry , catalysis , ion , metal , materials science , geotechnical engineering , fracture (geology) , metallurgy , engineering
Deprotonation of the 2‐cycloalkylbenzothiazolium perchlorates 1f ‐ h with sodium hydride in the presence of methanesulfonyl azide ( 3 ) affords the spirocyclic dihydro‐1,4‐benzothiazines 9f ‐ h together with small amounts of the 2‐iminobenzothiazole 5 . The 2‐cycloalkylidenedihydrobenzimidazoles 11e ‐ h are generated by deprotonation with potassium hydride from the corresponding 2‐cycloalkylbenzimidazolium salts 10e ‐ h , and trapped with 3 to yield the zwitterions 12e ‐ h . Whereas 12h is thermally unstable, 12e ‐ g are isolated and thermolysed at 20‐80 °C. The cyclopropyl zwitterion 12e decomposes in an ill‐defined way, only at temperatures above 80 °C. In contrast, 12f , g , and, in particular, 12h , decompose more readily to furnish the products of ring expansion ( 13f ‐ h ) and those of a [3 + 2] cycloreversion ( 6 and 14 ) of intermediate spirocyclic triazolines. Products that might be indicative of the intervention of hypothetical zwitterions of type 8 cannot be detected.