Diels-Alder catalysts Boron trifluoride etherate

DIELS-ALDER CATALYSTS Boron trifluoride. Boron irifluoride etherate. Ethylaluminum dichloride. Silica gel. Stannic chloride. Titanium(IV) chloride. Tris(p-bromophenyl)aminium hexa-chlorostibnatc. 

Diels-Alder catalysts Alkylaluminum halides, 5, 173 Boron trifluoride etherate, 43 Diethylaluminum chloride, 173 Dimethylaluminum chloride, 5 Sodium dodecyl sulfate, 281 Titanium(IV) chloride-Diethylaluminum chloride, 309... 

DIELS-ALDER CATALYSTS Alkylaluminum halides. Boron trifluoride etherate. Diaza-... 

Diel -AldeT catalyst. Kelly and Montury have examined the effect of three Lewis acids on the Diels-Alder reaction of perf-hydroxylated naphthoquinones with l-methoxy-3-methyl-l,3-butadiene magnesium iodide, boron trifluoride etherate, and boron triacetate. All three increase regioselectivity. BF, etherate and B(OAc)3... 

The synthesis of a soluble nonacenetriquinone based on the well-known Diels-Alder reaction of 1,3-diarylisoben-zofurans was developed by L.L. Miller and co-workers. The preparation of the 1,3-diarylisobenzofuran commenced with the Paai-Knorr furan synthesis. The substrate was an aromatic 1,4-diketone, which was treated with excess neat boron trifluoride etherate for almost two days to afford the desired 2,5-diarylfuran in almost quantitative yield. Interestingly, this cyclization could not be achieved efficiently by using the more traditional acid catalysts such as H2SO4 or PPA. 

Similar structures can be realised in low yield from the Friedel-Crafts reaction of 1,4-dimethoxybenzene with substituted phthalic anhydrides (R = Me, Et, i-Pr), which were obtained by the appropriate Diels-Alder synthesis. The acylations were effected in the presence of boron trifluoride etherate as catalyst, followed by demethylation of the product (ref.55). 

Boron trifluoride is a highly moisture-sensitive gas (31). It is utilized in esterification, ether formation, Friedel-Crafts alkylation and acylation, and Lewis acid-catalyzed Diels-Alder reactions. A more widely used, easy-to-handle and convenient liquid source of BF3 is boron trifluoride etherate [BF3-0(C2H5)2] (32). Its main usage as catalyst is in the direct esterification of all types of acids, rearrangements, aldol condensation, and Lewis acid-catalyzed Diels-Alder reactions. It is the most frequently used acid in epoxide ring opening and rearrangement (33). 

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