No abstract

isolated and fully characterized. Chromatographic analysis of the reaction mixture indicates that 12 is produced immediately upon addition of acetic acid to 11, whereas 8 is produced only upon warming the solution. The conversion of 11 to 12 may be formulated as an intramolecular Diels-Alder reaction of the protonated form of 11. The Diels-Alder reaction has been demonstrated with 11 itself, but it is slow in toluene at 110 °C.1 23456 The transformation of 12 into 8 is presumably a rr-cyclization of the prenyl double bond onto the immonium moiety of 12. It is noteworthy that the process is highly stereoselective with respect to the isopropenyl group and delivers 8 with the double bond situated only in the terminal position. We believe that a process such as this may be involved in the biosynthesis of the Daphniphyllum alkaloids.The total synthesis reported here is notable for its brevity and high yield; only nine laboratory operations are required from homogeranyl iodide, and the overall yield from this material is 44%. At the present time, we have prepared more than 3 g of 10 in this manner.

Unusually stable complexes are formed between [6]paraphenyleneacetylene ([6]CPPA, see picture) and fullerenes (either C60 or bis(ethoxycarbonyl)methanofullerene). Crystallographic analysis reveals that a major driving force for the formation of such complexes is the existence of a novel concave–convex π–π interaction (see structure).

A n p n . . Chein. Int. Ed. Enzl 1996, 35. N o . 22 C VCH Verlugs~eseli~~chuft nihH, 0-69451 Wernhrim, 1996 057n-OR33/96/3522-2665 S 15.00+ .Z.i:O

Reduction of NiX2(PPh3)2 with zinc in the presence of Et4NI gives a nickel catalyst which has been proven to be useful for the coupling of aryl halides. This nickel catalyst can be prepared in THF without an additional triphenylphosphine and is effective for the homocoupling of aryl chlorides, bromides, and iodides to produce biaryls and bipyridines in good yields. The reported new approach provides a simple access to novel derivatives of biaryls and bipyridines.