Preparation of New Heptafulvenes and the Related Compounds Derived from 2H-Cyclohepta[d]thiazol-2-one and -2-thione

Regioselective Nucleophilic Substitution of 5‐Bromo‐2‐methoxytropone

“…It is known that activated troponoids ( 1c ) and ( 1e ) reacted with thiourea to generate 2‐ S ‐substituted compounds ( 3 ) as HX salts (X = OTs and Cl). A thermal intramolecular cyclization of 3 and successive dehydration gave iminium salts ( 4a ), which were hydrolyzed to furnish 2 H ‐cyclohepta[ d ]thiazol‐2‐one ( 4b ) . Compound ( 4b ) has a unique reactivity and could be transformed into a novel heptafulvene as shown in Scheme .…”

“…That is, diethylamine, propylamine, and p-chloroaniline/triethylamine reacted with 2 under boiling conditions to give 2-aminotropones (10) [6b], (11), and (12), respectively. From the products analysis, it is found that 5-substitution of 2 and further one of the products (8)(9)(10)(11)(12) with the O-and N-nucleophiles did not proceed in these conditions. Next, we examined the reaction with Snucleophiles in expectation of the 5-selective substitution (Scheme 4, left).…”

“…A thermal intramolecular cyclization of 3 and successive dehydration gave iminium salts (4a), which were hydrolyzed to furnish 2H-cyclohepta[d]thiazol-2-one (4b) [8,9]. Compound (4b) has a unique reactivity and could be transformed into a novel heptafulvene as shown in Scheme 1 [9]. In expectation of conversion into a 5-bromo derivative (5b), we tried treatment of 2 with thiourea (Scheme 2).…”