Bradsher reaction

The intramolecular Bradsher cyclization refers to the acid-catalyzed aromatic cyclodehydration of ort/zo-acyl diaryImethanes to form anthracenes. On the other hand, the intermolecular Bradsher cycloaddition often involves the Diels-Alder reaction of a pyridium with a vinyl ether or vinyl sulfide. 

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 33, Springer-Verlag Berlin Heidelberg 2009 

Meth-Cohn, O. J. Chem. Soc., Chem. Commun. 1970, 1094-1095. 

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 38, Springer International Publishing Switzerland 2014 

Mondal, M Kerrigan, N. J. Bradsher Reaction, In Name Reactions for Carbocyclic Ring Formations, Li, J. J., Ed. Wiley Hoboken, NJ, 2010, pp 251—266. (Review). 

Anthracenes from ort/io-acyl diarylmethanes via acid-catalyzed cyclodehydration. 

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Boroxazothienopyridines, 4, 1029-1032 Borsche synthesis, 3, 44 Botrydiplodin mass spectrometry, 4, 585 Boulton-Katritzky rearrangement, 5, 288 Bovine milk xanthine oxidase substrates, 1, 234 Bradsher reaction... 

The condensation of thiophene with ketones in presence of 70% H2S04 gives di-2-thienylmethane derivatives (63AHC(l)l). Thus acetone leads to (85). Intramolecular versions of such acid-catalyzed condensations with aldehydes and ketones are known (Scheme 14) (73JOC1056, 70AHC(11)177). The Bradsher reaction has been used for the synthesis of thienobenzothiophenes in low to moderate yields (Scheme 15) (70CC1094). 

Allyl- and benzyl-thiophenes may be cyclized by a direct Bradsher reaction, using dichloromethyl methyl ether or related dichloroalkyl methyl ethers and tin(IV) chloride catalysis to give the corresponding benzo- or dibenzo-thiophenes in 55-60% yield (73JCS(P1)1099). Thus substituted thiophenes having a benzyl group at either the 2- or 3-position, e.g. (349), when treated with a 1,1-dichloroalkyl methyl ether and tin(IV)... 

Heterocyclic systems with one heteroatom. Condensed heteroaromatic cations are reactive in [2 + 4] cycloaddition reactions with inverse electron demand. For instance, 2-benzopyrylium salts 403 react with vinyl ethyl ether to afford naphthalene derivatives 405 in good yields via initial adducts 404 <1990KGS315>. Similar transformations (Bradsher reaction) are also known for isoquinolinium salts <1984CC761>. 

Bradsher reaction. Acid-catalyzed cyclodehydration of o-acyldiarylalkanes to polycyclic hydrocarbons and their heterocyclic analogs. 

C02Et derivative, respectively (direct Bradsher reaction).337 A substituted... 

As a synthetic method the Bradsher reaction per se appears to be superior to the Elbs reaction. The direct procedure of Meth-Cohn uses carcinogenic n-butyl dichloromethyl ether. The Castle procedure is relatively free of toxic reagents, isomeric precursors, and rearrangements, but numerous steps are involved before the Bradsher reaction is reached. Thus, all of these methods have advantages and shortcomings. 

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