Pawel Rempala

Quadrannulene: A Nonclassical Fullerene Fragment

The presence of nonhexagonal rings in an otherwise graphitic lattice induces curvature. Pentagons are common—twelve pentagons surrounded by hexagons make up C60. Larger rings are present in Stone–Wales defects, and the polyhedral formula of Euler mandates their existence in carbon nanotube Y-junctions. Except for a single, partially saturated example, four-membered rings in graphitic structures are, however, unknown. The smallest examples of these graphitic structures are the [n]circulenes, wherein a central n-sided polygon is surrounded by n-fused benzenoid rings. [7]Circulene, first prepared by Yamamoto, Nakazaki, and coworkers in 1983, is saddle shaped. [6]Circulene, or coronene, is the trivial, planar case, and it was first synthesized by Scholl andMeyer in 1932 but also occurs naturally. [5]Circulene, or corannulene, comprises 1/3 of the C60 skeleton and has been intensely studied, and it was first prepared by Lawton and Barth in 1971. Whereas a few pioneering attempts have been reported, [4]circulene has never been synthesized before. We report herein the preparation and characterization of a stable [4]circulene. By analogy with Lawton s naming of corannulene (Latin: cor, heart; annula, ring), we suggest the trivial name quadrannulene (Latin: quadra, square; annula, ring) for the [4]circulene parent. Hence, we name this derivative 1,8,9,16-tetrakis(trimethylsilyl)tetra-cata-tetrabenzoquadrannulene, abbreviated TMS4-TBQ. The IUPAC name and atom numbering are given in the Supporting Information. Our unoptimized five-step synthesis (Scheme1) provides TMS4-TBQ in very low yield. Hopf and co-workers recently summarized two synthetic strategies to the quadrannulene core: making the four-membered ring from [2,2]-paracyclo-

ADAMANTYLCHLOROCARBENE : CHARACTERIZATION AND REARRANGEMENT TO CHLOROHOMOADAMANT-3-ENE

Abstract Adamantylchlorocarbene and its ring-expanded product, chlorohomoadamant-3-ene, have been characterized by matrix isolation spectroscopy combined with DFT calculations.

Simulation of Actuation by Polymeric Polyelectrolyte Helicenes.

The potential of several peripherally substituted [6.3.1] helicenes to serve as linear actuators was investigated using molecular dynamics calculations. Reversible extension upon ionization of pendant functionality was observed in three of four cases. The largest extensions were obtained for molecules with amino groups or ionized phosphate groups attached directly to the helical backbone (extensions of 176 ± 4% and 184 ± 4%, respectively). Electrostatic forces and swelling drive the actuation.

Matrix isolation and photochemistry of 1- and 2-naphthylchlorocarbene

We have for the first time characterized the 1- and 2-naphthylchlorocarbenes by IR and UV/vis spectroscopy in N2 matrices at 10 K. Although evidence suggests the presence of predominantly only one geometric isomer in the case of the 1-naphthylchlorocarbene, the IR and UV/vis spectra of the 2-naphthylchlorocarbene indicate two distinct conformations. With selective irradiation, the longer-wavelength absorbing s-Z-isomer of 2-naphthylchlorocarbene can be photochemically driven to the alternate s-E conformation. Irradiation of the 1- and 2-naphthylchlorocarbenes induces cyclization to 7-chloro-4,5-benzobicyclo[4.1.0]hepta-2,4,6-triene and 7-chloro-2,3-benzobicyclo[4.1.0]hepta-2,4,6-triene, respectively. The cyclization can be reversed by irradiation at shorter wavelengths.Our results on the singlet naphthylchlorocarbenes photochemical ring-closures parallel observations of Chapman, McMahon, and co-workers on the parent triplet 1- and 2-naphthylcarbenes (P. R. West, A. M. Mooring, R. J. McMahon and O. L. Chapman, J. Org. Chem., 1986, 51, 1316; S. W. Albrecht and R. J. McMahon, J. Am. Chem. Soc., 1993, 115, 855). In particular, under matrix isolation conditions, the naphthylcarbenes appear to photochemically only cyclize to the corresponding cyclopropenes, which in turn only photochemically ring-open back to the carbenes. Ring-expansion in these systems to benzocycloheptatetraenes is not detected.