Benzopyrans Chromenes

A patent from Pfizer (15USP0274721) disclosed a preparation of (6-SF5-2H-chromen-4-yl)methanol (108) as an intermediate in a synthesis of 

An asymmetric cyclocondensation of S-SFs-salicylic aldehyde 114a or its bromo-substituted analog 114d with 4,4,4-trifluoro-2-butenal in the presence of a catalytic amount of (S)- or (R )-(—)-a,a-diphenyl-2-pyrtohdine-methanol trimethylsilyl ether and 2-nitrobenzoic acid gave related (S)- or 

---

The simple pyrans are rather unstable compounds and of little biological or industrial significance but some of their benzo derivatives are of considerable interest. Many 2H-1-benzopyrans (chromenes) are found in plants, for example evodionol (126), lapachenole (127), lonchocarpin (128), rottlerine (129) and edulan (130). A few of the constituents of marijuana (hashish) belong to this class, for example cannabinol (131). 

A. C. Shekhar, A. R. Kumar, G. Sathaiah, K. Raju, P. S. Rao, M. Sridhar, B. Narsaiah, P. V. S. S. Srinivas, B. Sridhar, Helv. Chim. Act. 2012, 95, 502-508. An efficient one-pot synthesis of substituted 17/-naphtho[2,l-h]pyrans and 47/-l-benzopyrans (chromenes) under solvent-free microwave-irradiation conditions. 

---