Friedel-Crafts cyclization, improved

Chloro-10 9-borazarophenanthrene has been obtained only by Friedel-Crafts cyclization of the adduct from 2-aminobiphenyl and boron trichloride 2 the procedure described here is an improvement on the original process,2 in which no solvent was used. 

Acid chloride—olefin addition and Friedel-Crafts cyclization A previous procedure was improved by use of methylene chloride as solvent rather than carbon disulfide. To check the progress of the reaction, one can quench a 2 3-ml. aliquot with water in a test tube, separate and dry the organic phase, and evaporate. The infrared spectrum will show disappearance of the acid chloride carbonyl band at 5.6(1 /j and appearance of the... 

All Improved Synthesis of the Keto-Furan An Efficient Friedel-Crafts Cyclization... 

Stannic Chloride pn the Free Acid. Ring closure by heating the free acid with stannic chloride at 100-120° has been shown to be successful on several types of acids.85 47> 8 88 80, 189 819 These and some other acids which have been cyclized by this method may be found in Table XI. In four instances (items 3, 7, 14, 17) stannic chloride treatment gave better results than sulfuric acid. Eleven of the acids in Table XI (items 3, 5, 8, 9, 10,12, 13, 14, 16, 17, 18) have been cyclized also by the Friedel-Crafts method on the acid chloride. With seven acids (3, 6, 8, 9, 12, 14, 17) the yields were better, while with four (5, 10, 16, 18) they were lower, than with stannic chloride. Except for one (18) of these latter acids, however, there seems to be some question as to whether the optimum conditions for the Friedel-Crafts reaction were employed. Of the acids (4, 6,12) which have since been cyclized with hydrogen fluoride, considerable improvement in yields was realized. 

Another Friedel-Crafts route to phenanthrenes is the Bardhan-Sengupta phenanthrene synthesis. When phenethylcyclohexanol 222 was cyclized with phosphorus pentoxide at 140°C, the product was 223. Aromatization was accomplished by heating with selenium to give the phenanthrene derivative 224 (1-methyl-7-isopropylphenanthrene, otherwise known as retene). An improvement in the reaction used hydrogen fluoride (HF) to induce cyclization.l ... 

Non-chloroaluminate ILs, which are in general poor nucleophiles, have proven to be attractive alternative media for Lewis acid catalyzed reactions. ILs may have a reaction rate accelerating effect, and they may improve selectivity and facilitate catalyst recovery. This is the case for scandium triflate catalyzed Diels-Alder cycloaddition [8,9], three-component (aldehyde, aniline, triethylphosphite) synthesis of a-aminophosphonates [10], Claisen rearrangement and cyclization reactions [11], or Friedel-Crafts reactions [12, 13]. 

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