Chromanone alkaloids

Quite recently, the use of natural cinchona alkaloids as catalysts for the intramolecular oxo-Michael addition of o-tigloylphenol (3), furnishing chiral ris-2,3-dimethyl-4-chromanone 4, which is a valuable intermediate for the synthesis of the anti-HIV-1 active coumarins, (+ )-calanolide A (5a), and (+ )-inophyllum B (5b), was reexamined by Ishikawa and coworkers (Scheme 9.2) [2], The parent cinchona alkaloids,... 

Thiourea catalyst with a modified cinchona alkaloid unit is applied to intramolecular Michael addition of phenol chiral chromanone is produced in high yield with good... 

Alkaloid 1 also catalyzed the asymmetric intramolecular oxo-Michael addition of o-tigloylphenol in chlorobenzene, leading to ctx-2,3-dimethyl-4-chromanone (Scheme 6.3) [18], a valuable intermediate in the total synthesis of (+)-calanoUde A and (+)-inophyllum B. 

In 2007, Scheidt reported an intramolecular oxa-Michael reaction of a-substituted chalcones 114 catalyzed by cinchona alkaloid derived thiourea 113. Chromanones 115 were efficiently produced after an acid-promoted decarboxylation process (Scheme 36.31) [39a]. 

---