Chien-Hong Cheng

Stereoselective [2 + 2 + 2] cocyclotrimerization of oxa- and azabenzonorbornadienes with alkynes catalyzed by nickel complexes: first transition metal-mediated synthesis of isobenzofuran and isoindole precursors

Oxabenzonorbornadiene (1a) reacted with various alkynes in the presence of Ni(PPh3)2Cl2, PPh3 and zinc powder in toluene to give two common products 2a and 2b regardless of the alkyne used. The formation of 2a and 2b are proposed to be from the Diels–Alder reaction of 1a and isobenzofuran. The latter is generated from the retro Diels–Alder reaction of [2xa0+xa02xa0+xa02] cycloadducts of 1a and alkynes catalyzed by the nickel system. A series of nickel-catalyzed [2xa0+xa02xa0+xa02] cycloadducts (4a–j and 5a–d) of oxa- and azabenzonorbornadienes (1a–d) with terminal alkynes were isolated at temperatures −5–18xa0°C. Similarly, hepta-1,6-diyne and octa-1,7-diyne reacted with 1a and 1d to give novel pentacyclic [2xa0+xa02xa0+xa02] cycloadducts 6a–d in 62–75% yields. These products are convenient isobenzofuran and isoindole precursors that react with various dienophiles to afford the corresponding Diels–Alder adducts. In addition, the [2xa0+xa02xa0+xa02] cycloadducts may be used as precursors for the synthesis of aromatic compounds. For example, the reaction of 1a with methyl but-2-ynoate catalyzed by the nickel system provided aromatic compound 3 in 94% yield. In this reaction, 1a is a ‘masked acetylene’ providing an acetylene moiety to 3.

Interaction of magnesium and lithium ions with [60]fullerene derivatives bearing a phosphorus ylide group

[60]Fullerene derivative 1 containing of an α-ylide group exists as a mixture of E and Z isomers. Treatment of 1 with MgBr2 or LiI in CDCl3 under ultrasonic agitation gave an adduct in which the carbonyl oxygen of α-ylide ester moiety in 1 is coordinated to the metal ion. The NMR spectra show that the adducts exist as a single isomeric form. After ultrasonic agitation, the adducts gradually revert to the original E,Z-mixture owing to slow absorption of moisture. Further ultrasonic treatment of the mixture resumes the complexation as long as enough anhydrous metal halides are still present.