Dibenzopyrans, synthesis

Intramolecular cyclization of 2-lithiobenzyl-2-halophenyl amines, ethers, and thioethers—Synthesis of phenanthridine, dibenzopyran, and dibenzothiopyran derivatives Having demonstrated the efficiency of this methodology for the preparation of indole derivatives, we prepared the 2-fluoro-phenyl ether and thioether 22 a, b to study their potential as substrates that could afford oxygen and sulfur heterocycles. However, treatment of 22 a, b with fBuLi afforded, after... 

Adams R, Baker BR, Wearn RB, Structure of Cannabinol. 111. Synthesis of Cannabinol,l-Hydroxy-3-n-amyl-6,6,9-trimethyl-6-dibenzopyran, J Amer Chem Soc 62 2204-2207 1940. 

Formation of the isochroman system is considered to trigger the synthesis of the dibenzopyran (17, X = H2) by the acid catalysed cyclisation of c/s-enediynes (16, X = H2). In a similar manner, the carboxyl function in (16, X = O) promotes cylisation to a dihydropyranone derivative which is followed by a Myers cycloaromatisation to the dibenzopyranone (17, X = O) (95TL9165). 

While using o-bromophenol as the ort/w-arylating agent in the above sequence, Catellani found the product to be a 67/-dibenzopyran, the product of an ortho-arylation/Mizoroki-Heck coupling followed by an oxy-Michael addition of the phenol to the electron-deficient alkene. This was later developed into an efficient method for the synthesis of a variety of 6//-dibenzopyrans (Scheme 21) [56, 57], and is one of the most modular and effective methods to construct this interesting heterocyclic framework. 

Lately, Catellani and coworkers [83] have described a similar process for the synthesis of 6//-dibenzopyran derivatives 147. They investigated the reaction of o-bromophenols 145, iodoarenes and acceptor-substimted alkenes in the presence of norbomene. The... 

Motti, E., Faccini, F., Ferrari, 1. et al. (2006) Sequential unsymmetrical aryl coupling of -substituted aryl iodides with o-hromophenols and reaction with olefins paUadium-catalyzed synthesis of 6//-dibenzopyran derivatives. Org. Lett., 8, 3967-70. 

---