Thioamides as useful synthons in the synthesis of heterocycles.

Synthesis of some new pyrazolo[3,4-d]pyrimidine derivatives of expected anticancer and radioprotective activity

A catalyst system comprising palladium acetate−bidentate phosphine is effective for the cyclocarbonylation of o-iodoanilines with heterocumulenes at 70−100 °C for 12−24 h to give the corresponding 4(3H)-quinazolinone derivatives in good yields. Utilizing o-iodoaniline with isocyanates, carbodiimides, and ketenimines for the reaction, 2,4-(1H,3H)-quinazolinediones, 2-amino-4(3H)-quinazolinones and 2-alkyl-4(3H)-quinazolinones were obtained, respectively. The nature of the substrates including the electrophilicity of the carbon center of the carbodiimide, and the stability of the ketenimine, influence the product yields of this reaction. Urea-type intermediates are believed to be generated first in situ from the reaction of o-iodoanilines with heterocumulenes, followed by palladium-catalyzed carbonylation and cyclization to yield the products.

Palladium-catalyzed cyclocarbonylation of o-iodoanilines with heterocumulenes: regioselective preparation of 4(3H)-quinazolinone derivatives

An efficient route to N(4)-substituted 2,4-diaminoquinazolines has been developed by employing tandem condensation of cyanoimidate-amine and reductive cyclization in iron-HCl system. This method is tolerant of a following intramolecular N-alkylation and produces two fused heterocycles in a one-pot procedure. This protocol is a facile two-step synthesis of tricyclic quinazolines, which is effected by potent cyanoimidation and tandem reductive cyclization from 2-nitrobenzaldehydes. Moreover, the forming process of tricyclic quinazolines has been investigated from the ring-opening/ring-closing cascade point of view. It is found that the preparation of tricyclic quinazolinones in good yields relies on the selective hydrolysis of tricyclic quinazolines in base or acid system.

William D. Dean

Papers

Synthesis of 4(3H)‐quinazolinones from derivatives of methyl 2‐isothiocyanatobenzoate