Diaryne equivalents

Wittig and Harle were the first to use tetrahaloarenes as diaryne equivalents.3 From 1,4-dibromo-2,5-difluorobenzene, butyllithium and furan (in THF) they isolated the mono- and bis-adducts shown. 

Similar sequences starting with appropriate 1,2,3,4-tetrahaloarenes (1,3-diaryne equivalents) yield hindered phenanthrenes.9 Cyclopentadienes,7 fulvenes,7 isoindoles,7 anthracenes10 and other dienes11 have also been used as diaryne traps. 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

Polyhalogenated arenes can function as diaryne equivalents via the tandem sequence illustrated in Scheme lO.90-91 The predominant meta addition to aryne (59) can be ascribed to steric hindrance, while in addition to (58) both steric and electronic effects favor the observed regioselectivity. 

A number of new diaryne equivalents have been developed by Hart et al. [137b, 142] in recent years. These very versatile reagents enable the synthesis of large polycyclic hydrocarbons in very few steps. The pentiptycene 85, for exam-... 

G.C. The dilithiation mechanism in the reactions of polyhaloarenes as diaryne equivalents. Tetrahedron Lett. 1983, 24, 5721-5724. (e) Blatter, K Schlueter, A.-D. Model studies for the synthesis of ribbonshaped structures by repetitive Diels-Alder reaction. Chem. Ber. 1989, 122, 1351-1356. 

Bis-arynic reagents in which the two arynes are in separate, insulated arene rings have also been developed. For example, bis-anthranilic acid 478 is a synthetic equivalent for diaryne 479 aprotic diazotization of 478 in the presence of various dienes (i.e., tetraphenylcyclone, 2,5-dimethylfuran, anthracene) gave the expected bis-adducts in 40-... 

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