Palladium-catalyzed sixfold coupling of hexabromobenzene (20) with a variety of alkenylboronates and alkenylstannanes provided hexaalkenylbenzenes 1 in up to 73 % and 16 to 41 % yields, respectively. In some cases pentaalkenylbenzenes 21 were isolated as the main products (up to 75 %). Some functionally substituted hexaalkenylbenzene derivatives containing oxygen or sulfur atoms in each of their six arms have also been prepared (16 to 24 % yield). The sixfold coupling of the less sterically encumbered 2,3,6,7,10,11-hexabromotriphenylene (24) gave the desired hexakis(3,3-dimethyl-1-butenyl)triphenylene (25) in 93 % yield. The first successful cross-coupling reaction of octabromonaphthalene (26) gave octakis-(3,3-dimethyl-1-butenyl)naphthalene (27) in 21 % yield. Crystal structure analyses disclose that, depending on the nature of the substituents, the six arms are positioned either all on the same side of the central benzene ring as in 1 a and 1 i, making them nicely cup-shaped molecules, or alternatingly above and below the central plane as in 1 h and 23. In 27, the four arms at C-1,4,6,7 are down, while the others are up, or vice versa. Upon catalytic hydrogenation, 1 a yielded 89 % of hexakis(tert-butylethyl)benzene (23). Some efficient accesses to alkynes with sterically demanding substituents are also described. Elimination of phosphoric acid from the enol phosphate derived from the corresponding methyl ketones gave 1-ethynyladamantane (3 b, 62 % yield), 1-ethynyl-1-methylcyclohexane (3 c, 85 %) and 3,3-dimethylpentyne (3 e, 65 %). 1-(Trimethylsilyl)ethynylcyclopropane (7) was used to prepare 1-ethynyl-1-methylcyclopropane (3 d) (two steps, 64 % overall yield). The functionally substituted alkynes 3 f-h were synthesized in multistep sequences starting from the propargyl chloride 11, which was prepared in high yields from the dimethylpropargyl alcohol 10 (94 %). The alkenylstannanes 19 were prepared by hydrostannation of the corresponding alkynes in moderate to high yields (42-97 %), and the alkenylboronates 2 and 4 by hydroboration with catecholborane (27-96 % yield) or pinacolborane (26-69 % yield).

COMMUNICATIONS 4.9(1) and 6.1(1)'; average interplane distance 3.37(9) and 3.44(11) A).The Ag-N bond lengths are not significantly different in the two complexes, and the conformations of the bis(oxazo-1ine)pyridine units are virtually superimposable in [Ag,(2)J2 + and [Ag3(3)333'. The only reasonable explanation of the remarkable difference in structure is the existence of the stacking interaction in [Ag,(3)J3 + ; although stacking interactions have frequently been observed in helicates,", 21 this is to our knowledge the first example in which their absence or presence appears to modify the structure. We may note that although the complexation of the silver ion by the ligands provides the thermodynamic driving force for the assembly, the use of monodentate ligands gives a freedom of rotation around the Ag-N bond that is absent in the case of complexation of a metal by bi-or tridentate ligands; it is therefore possible for the system to rearrange itself in such a way as to maximize the secondary stacking energy without imposing too great a strain upon the coordinate bond. This contrasts with a previous study in which the formation ofdouble or triple helices with a given ligand was controlled by the metal ion coordination preferen~e."~' The close stacking in [Ag,(3),](BF4), results in a very compact structure that crystallizes in a cubic space group, and has a crystal density 8 % greater than [Ag,(2),](BF4), . In solution, however, the trimeric cation appears to be unstable, the ES mass and 'H NMR spectra suggesting that partial dissociation to [Ag,(3),lZ + occurs. This question is currently being investigated. Exper imen t d Sect ionLigands 2 and 3 were prepared according to references [8,9]. In a typical procedure for the preparation of complexes, the ligand (0.5 mmol) in dichloromethane (5 mL). and AgBF, (0.5 mmol) in methanol ( 5 mL) were mixed and stirred for 15 min. The solution was evaporated to dryness, and the residue taken up in acetonitrile (5 mL). After filtration to remove the insoluble material, crystals were obtained by diffusion of diethyl ether.[Ag2(2)J(BF,J2. M.p. 205-210°C (decomp); elemental analysis calcd for Ag,

Schalenförmig ist Hexakis(3,3‐dimethyl‐1‐butenyl)‐benzol 1 (Kalottenmodell siehe rechts), das durch die Palladium‐katalysierte Kupplung von Hexabrombenzol mit 2‐(3,3‐Dimethyl‐1‐butenyl)‐1,3,2‐benzodioxaborol zugänglich ist. Im Molekül weisen alle sechs Alkenylgruppen zu einer Seite der Benzolringebene. Durch katalytische Hydrierung von 1 erhält man das entsprechende Hexakisalkylbenzol, das in säulenförmigen Stapeln kristallisiert, wobei die Alkylgruppen alternierend zu beiden Seiten der Benzolringebene weisen und gestaffelt angeordnet sind.

The bowl-shaped hydrocarbon hexakis[(E)-3,3-dimethyl-1-butenyl]benzene (HB) has been cocrystallized with either C 60 or C 70 to form clamshell-like assemblies with the fullerenes residing within the concave surfaces of two HB molecules. The structures of these two crystals have been determined by singlecrystal X-ray diffraction. The HB molecules exhibit back-to-back stacking and close contacts in both cocrystals. This trait is remarkably similar to the packing seen in cases in which fullerenes cocrystallize with M II (OEP), where OEP is the dianion of octaethylporphyrin and M is generally Ni or Co. The C 60 structure features an ordered cage with a disordered solvent position, while the C 70 structure exhibits two orientations of the cage, all other components being ordered.

hydrocarbons hydrocarbons (benzene compounds) Q 0080 -094Palladium-Catalyzed Sixfold Alkenylation of Hexabromobenzene: An Interesting Case of Self-Organization.--(PRINZ, P.; LANSKY, A.; HAUMANN, T.; BOESE, R.; NOLTEMEYER, M.; KNIERIEM, B.; DE MEIJERE, A.; Angew.