Friedel-Craft-like cyclization

Triflic anhydride has been shown to activate enones (113) with an electron-rich aromatic pendant to undergo a Friedel-Crafts-like cyclization, affording the cyclic enol triflate (114).170... 

Our synthesis of the 7-hydroxy-substituted isoflavanones la-e had to take into account protection of hydroxy group due to the likely interference with the synthetic route and in particular the key decarboxylative asymmetric protonation step. The synthesis of la-c could be accomplished by a series of Pb-mediated arylations of allyl-P-keto ester 7. This was accessed by Friedel-Crafts acylation, cyclization, NAP-protection and subsequent acylation with allyl cyanoformate (Scheme 5.2) [19-21]. We were able to generate isoflavanone precursors 8a-e from the allyl-P-keto ester (7) by introducing various aryl groups through the use of... 

Two mechanisms can be envisioned for the Pechmann condensation (1) acid-catalyzed transesterification of the P-keto ester followed by acid-catalyzed cyclodehydration of the resulting aryl acetoacetate (4), or (2) acid-catalyzed Friedel-Crafts-like phenol alkylation ortho to the phenolic hydroxyl group) followed by intramolecular transesterification/cyclization of the resulting o-hydroxycinnamic acid ester (5). 

As alluded (vide supra), some confusion may arise with respect to this named reaction as there is reference in the literature to an alternative reaction with the same name. The Bradsher reaction forms aromatic rings but via an acid-catalyzed Friedel-Crafts-like process. Thus diaryl-methanes having a carbonyl group in the ortho position can undergo a cyclodehydration reaction to generate the corresponding anthracene derivatives. In this respect, the Bradsher reaction is related to the Elbs reaction, which involves the pyrolytic cyclization of diaryl ketones 6 having an ortho methyl or methylene substituent for the formation of polycyclic aromatics 7. 

A total synthesis of dihydrolycorine (85), y-lycorane (87) and 8-lyco-rane (92), has been achieved starting from the indanone carboxylic acid 77. This, in turn, was obtained, like the tetralone ester 76, from the known anhydride (75) via Friedel-Crafts cyclization of the monomethyl esters obtained from 75 by treatment with 1 mole of methanol. Reduction of the methyl ester of 77 (LiAlH4), followed by Mn02 oxidation,... 

The use of alkenes as sources of electrophiles in Friedel-Crafts alkylations has also been studied. The intramolecular alkylation of l-(2-tolyl)-( )-pent-3-ene gives 1,5-dimethyl-l,2,3,4-tetrahydronaphthalene in 95 % yield [55]. BF3 has been shown to form a complex with nitromethane which is particularly effective in catalyzing proton-initiated cascade cyclization like that shown in Eq. (29) [56]. 

Schemes aimed at the construction of elaborate two-dimensional -PAHs with boron at their center represent the cutting edge in synthetic methodology toward well-defined graphene-like materials with atomically precise 5-doping (Section 10.4.2.2). Yamaguchi and coworkers showed that oxidative (Friedel-Crafts/Scholl-type reactions) or radical-based cyclizations of triarylboranes with reactive pendant functionalities could be used to fuse the 5-aryl groups into planar arrays. The seminal synthesis of a planarized dibo-raanthracene (Scheme 10.7) is representative of the oxidative/acid-catalyzed approach [24]. Installation of pendant 2,6-di(2-propenyl)phenyl groups via...

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