Coumarins, ring synthesis from phenols

Ring synthesis of coumarins 9.3.2. / From phenols and 1,3-ketoesters... 

One of the most reliable and widely used syntheses of coumarins involves the acid-catalyzed reaction between a phenol and a jS-keto ester, the Pechmann reaction (45CRV(36)1, 530R(7)l). An important aspect of the reaction is that it shows a dependency on all three reactants, which can be varied widely, thereby optimizing both the scope and conditions of the synthesis. As a consequence, satisfactory yields of coumarins substituted in either the benzene or pyranone ring or both rings can be obtained from readily accessible starting materials. 

A number of heterocyclics such as coumarins, flavones, and quino-lones have been prepared from o-subst. co-(methylsulfinyl)aceto-phenones . A simple isoindole synthesis with hydrazines has been published Phenolic coupling with PdCl2 has been used efficiently to produce carpanone whereby five contiguous asym. centers with the correct stereochemistry have been introduced in a single step . A facile synthesis of the tetracyclic skeleton of rheadan alkaloids, whidi have a characteristic azepine ring, has been reported Benzimidazoles and benzoxazoles have been prepared by a novel ring closure of a-amino-/9,7-ethylenenitriles . ... 

---