Royal Society of Chemistry Aromatic & Heteroaromatic Chemistry, Vol 4: Volume 4 (Specialist Periodical Reports - Aromatic and Heteroaromatic Chemistry)

Excerpt. © Reprinted by permission. All rights reserved. Aromatic and Heteroaromatic Chemistry Volume 4A Review of the Literature Abstracted between July 1974 and June 1975By C. W. Bird, G. W. H. CheesemanThe Royal Society of ChemistryCopyright © 1976 The Chemical SocietyAll rights reserved.ISBN: 978-0-85186-783-0ContentsChapter 1 Ring Systems of Topical Interest By P. J. Garratt, 1, Chapter 2 Intermolecular and lntramolecular Cyclization Reactions in Ring Synthesis By P. A. Lowe and A. W. Somerville, 59, Chapter 3 Cycloaddition Reactions By G. V. Boyd, 106, Chapter 4 Ring Transformations By H. C. van der Plas and J. W. Street, 146, Chapter 5 Electrophilic Substitution on Carbon By R. Taylor, 227, Chapter 6 Electrophilic Substitution on Heteroatoms By J. H. Lister, 261, Chapter 7 Nucleophilic Substitution By G. B. Barlin, 277, Chapter 8 Aromatic Substitution by Free Radicals, Carbenes, and Nitrenes By S. R. Challand, 296, Chapter 9 Addition Reactions By G. V. Boyd, 317, Chapter 10 Ring-cleavage Reactions By T. L. Gilchrist, 360, Chapter 11 Reactions of Substituents By B. C. Uff, 374, Chapter 12 Porphyrins and Related Compounds By K. M. Smith, 397, Chapter 13 Naturally Occurring Oxygen-ring Compounds By R. D. H. Murray, 414, Chapter 14 Other Naturally Occurring Compounds By J. R. Lewis, 442, Author Index, 485, CHAPTER 1Ring Systems of Topical InterestBY P. J. GARRATT1 IntroductionThe general organization of this chapter is the same as that used in the previous volumes. A collection of reviews on non-benzenoid aromatic chemistry has appeared. Herndon and Ellzey have shown that the appropriate use of resonance structures leads to qualitative results in good agreement with SCF calculations. Graph theory has been applied to an analysis of the orbital levels in conjugate hydrocarbons. Calculations of the diamagnetic susceptibilities of non-alternant hydrocarbons have been made, and a geometric correction has been applied to calculations of ring current. Maier has reviewed recent work on cyclobutadiene and tetrahedrane, to which his group have made important contributions. Cyclopropanol chemistry has been reviewed.2 Valence IsomersAn ab initio study of tetrahedrane (1) suggests that it is a local minimum on the (CH)4 surface. The C-C bond lengths were calculated to be 1.48 Å, and the C — H bonds 1.05 Å. A gas-phase electron-diffraction study of benzvalene (2) has been reported, and the derived bond lengths and angles are in good agreement with those obtained in the microwave study (see Vol. 3, p. 2). The Raman spectra of (2) and of Dewar-benzene (3a) have been reported. The i.r., Raman, and photoelectron (p.e.) spectra of hexa-methyl-Dewar-benzene (3b) have been obtained, and bond orders of 0.87 for C(1) — C(4), 1.64 for C(2) —C (3), and 1.0 for C(1) — C(2) are suggested. A gas-phase electron-diffraction study of hexafluoro-Dewar-benzene (3c) gave bond lengths of 1.597 [C(1) — C(4)], 1.503 [C(1) — C(2)], and 1.356 A [C(2) — C(3)], and [angle] C(6)C(1)C(2) is 115.3°. A similar study on hexamethylprismane (4) gave C(1) — C(2) 1.540 and C(2) — C(3) 1.551 A, using the author's preferred model. The preparation of benz-valene is now available from Organic Syntheses. Benzvalene (2) reacts with di-imide to give dihydrobenzvalene (5), which at 240°C is transformed into hexa-1,3-diene (6) (Scheme 1). Ozonolysis of (2) gave the ozonide (7), which on treatment with LiAlH4 gave the bicyclobutane (8). Thermolysis of the carbene adducts (9) (see Vol. 2, p. 3) gave the olefin (10), and thermolysis of (10c) in TMEDA at 135°C gave (11). The reaction of (2) with dichloroketen gave (12), which on reduction with triphenyltin hydride gave the ketone (13a). The lithium salt of the corresponding tosylhydrazone (13b) was pyrolysed to the (CH)8 hydrocarbon (14), a valence isomer of cyclo-octatetraene (Scheme 1).The bicyclopropenyls (15a, b) were rearranged by Ag1 ions to the Dewar-benzenes (16a — c). The reaction of hexamethyl-Dewar-benzene (3b) with dic