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Preparation of 2‐substituted 1,3,4‐thiadiazoles and mesoionic 1,3,4‐thiadiazole[3,2‐ c ]quinazolines from 4 H ‐3,1‐benzothiazine‐4‐thiones or 3‐amino‐4(3 H )‐quinazolinethiones
Author(s) -
Molina Pedro,
Arques Antonio,
Cartagena Inmaculada,
Alías María Asunción,
de la Concepción FocesFoces María,
Cano Felix Hernandez
Publication year - 1988
Publication title -
liebigs annalen der chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0170-2041
DOI - 10.1002/jlac.198819880206
Subject(s) - mesoionic , thiadiazoles , chemistry , ketene , hydrochloric acid , methylene , benzothiazine , medicinal chemistry , ring (chemistry) , stereochemistry , organic chemistry
Reaction of 4 H ‐3,1‐benzothiazine‐4‐thiones 1 with S ‐methylisothiosemicarbazide hydroiodide yields 2‐amino‐1,3,4‐thiadiazoles 2 instead of the expected 1,2,4‐triazolo[3,2‐ c ]quinazolines. Structures of compounds 2 have been established by means of 13 C‐NMR analysis and X‐ray crystallography. 3‐Amino‐4(3 H )‐quinazolinethiones 4 react with ketene dithioacetals 5 to give the new mesoionic 1,3,4‐thiadiazolo[3,2‐ c ]quinazolinylium‐2‐methanides 6 which undergo ring opening by the action of hydrochloric acid to give 2‐methylene‐1,3,4‐thiadiazoles 7 . Compounds 2 are converted into the corresponding oxygen analog 9 by treatment with hydrochloric acid.