The palladium-catalyzed coupling of haloarcnes and haloalkenes with alkenes. which was discovered by Richard F. Heck in the late sixties, has been a topic of fluctuating interest; however. in the last six years activity in this area has flourished. Careful choice of substrates and skillful tailoring of reaction conditions lead to impressive sequences consisting of even different reaction types that occur not only in a consecutive mode, but also i n a single operation. The wellestablished Heck reaction. together with other inechanistically related palladiumcatalyzed transformations with arene, alkene. and alkyne derivatives. opens the door to a tremendous variety of elegant and highly convergent routes to structurally complex molecules. The reaction is not disturbed by heteroatoms such as oxygen and nitrogen (nor by sulfur and phosphorus with some limitations). The spectrum of recent achievements starts with a range of chemoselective and regioselective monocouplings of highly functionalized substrates with unsymmetrical and multisubstituted reaction partners. Other advances include cascade reactions in which three. four, five, and even eight new C-C bonds are formed to yield oligofunctional and oligocyclic products with impressive molecular complexity. Even the enantioselective construction of complex natural products with quaternary stereocenters has been achieved with Heck reactions in key steps. as exemplified by the synthesis of crinan, picrotoxinin, and morphine. Today. the Heck reaction is indispensible in the arsenal of synthetic methods available to organic chemists. Certainly it is only a

Isolable quantities of C60, the smallest stable fullerene, have been synthesized in 12 steps from commercially available starting materials by rational chemical methods. A molecular polycyclic aromatic precursor bearing chlorine substituents at key positions forms C60 when subjected to flash vacuum pyrolysis at 1100 degrees C. No other fullerenes are formed as by-products. The methods we have developed for the target-specific synthesis of fullerenes, applied here to a synthesis of C60, should make possible the directed laboratory preparation of other fullerenes as well, including those not accessible by graphite vaporization.

[structure: see text] Several DFT methods were found to be unreliable for computing hydrocarbon isomer energy differences. The errors grow with system size up to 20 kcal mol(-1) for the relative energies of the (CH)12 isomers; octahedrane is the most stable (CH)12 hydrocarbon. While DFT geometries generally are good, problems arise for structures with single bonds only, especially for small rings. We recommend the use of higher level, non-DFT energy single points computed at DFT-optimized structures.

Dedicated to Professor Wolfgang Liittke on the occasion of his 60th birthdayAmong the cyclic compounds of carbon, cyclopropane and its derivatives are outstanding by virtue of their unusual structural, spectroscopic, and chemical properties. The cyclopropane ring more closely resembles the C=C double bond than the cyclobutane ring: it is a small ring with "double bond character". Cyclopropyl and vinyl groups interact with neighboring T-electron systems and p-electron centers; both cyclopropane derivatives and olefins form metal complexes, and add strong acids, halogens, and ozone; they both undergo catalytic hydrogenation and cycloadditions. While distinct differences in reactivity do exist-the double bond usually being more reactive than the three-membered ring-there are no fundamental differences in behavior.-Although cyclopropane derivatives have been known for more than 90 years, intensive studies have been limited to the past 25 years. The development of carbene chemistry has rendered cyclopropane derivatives far more readily accessible. In recent years, the synthetic potential of the small-ring function has been increasingly exploited. A considerable number of newly developed methods utilizing this approach clearly demonstrates that the reactivity of the cyclopropene ring, like that of the C-C double bond, qualify it as a "functional carbon group". This development is in full swing; we may therefore justifiably devote considerable effort to the study of cyclopropane chemistry.Volume 18 . Number 1 1November 1979 Pages 809-886 The Chemical Bond in the Cyclopropane RingOlefins and cyclopropane derivatives are related in many ways"'. The reason for this lies in the similarity of bonding in the C-C double bond and in the three-membered carbon ring. There are two equivalent descriptions for each system. According to the MO model of Walsh[2] (see Fig. I), three occupied molecular orbitals (MOs) determine the nature of the C-C bonds of the three-membered ring. Of these, the orbit- 809a1 of lowest energy (cr) is a linear combination of three sp2-hybrid atomic orbitals (AOs), while the other two (es and e,) are equal-energy linear combinations of three p-AOs differing only in their symmetry properties. This picture is strongly reminiscent of the commonest description of a C-=C double bond by two occupied MOs, one linear combination each of two sp2 AOs (a-MO) and two p AOs (a-MO) (see Fig. 1). By analogy with the latter MOs, the Walsh es and eA orbitals are also called n or "quasi T" orbitals of the three-membered ring.The second kind of theoretical description is the valence bond (VB) model of cyclopropane, due originally to Forsterf3I and refined by C o u l~o n [~~. The C -C bonds are described as resulting from the overlapping of two sps-hybrid orbitals at each C atom (see Fig. 2). Since the directions of the orbitals cannot coincide with the directions of bonding, but are directed outwards relative to the latter, the bonds create the impression of being bent. However, this merely expresses the experimentally esta...