Benzannelated annulenes. II. The synthesis of trans-12b,12c-dimethyl-12b,12c- dihydrobenzo(e)pyrene. An indication of the exceptional aromaticity of the 15,16-dimethyldihydropyrene system

Abstract

The synthesis of trans-126,12c-dimethyl-126,12c-dihydrobenzo(e)pyrene 4, in 10 steps from o-dibromobenzene and 2,6-dichlorotoluene utilizing a Wittig rearrangement -Hofmann elimination sequence on the benzothiacyclophane 6 is described. The diatropicity of 4 is compared to the parent trans-10b,10c-dimethyl-10b,lOc-dihydropyrene 1, and to other benzannelated annulenes.REGINALD H. MITCHELL et JOSEPH SHUE-HEN YAN. Can. J. Chem. 55,3347 (1977).On decrit la synthkse comportant 10 Ctapes du dimethyl-12b,l2c dihydro-126,12c benzo(e)pyrene trans 4 a partir du o-dibromobenztne et dichloro-2,6 toluene en utilisant une sequence comportant un rearrangement de Wittig et une elimination d'Hofmann sur le benzothiacyclophane 6. La diatropicite de 4 est comparee a une molCcule analogue le dimethyl-106,lOc dihydro-106,lOc pyrene trans 1 et ti d'autres annulenes benzanneles.[Traduit par le journal] I Like benzene, trans-15,16-dimethyl-15,16-dihydropyrene 1 has both a (4n + 2)-n electron periphery and two identical KekulC structures and, moreover, since models indicate the macro-I ring of 1 to be nearly planar, it could reasonably be expected to be aromatic. The synthesis of 1 by Boekelheide and Phillips (2) confirmed this point, and in its 'H nmr spectrum, 1 showed its internal methyl protons to be exceptionally shielded at z 14.25 by the strong diamagnetic ring current. A more recent (3) synthesis of 1, utilizes the ready conversion of [2,2]metacyclophane-1,9-diene 2 into the thermodynamically (4) more stable photoisomer 1. In this conversion, the delocalization of the electrons in both the benzene rings has to be interrupted in order 'For part I, see ref. I.2Chemical Abstract name is now trans-106,lOc-dimethyl-106,lOc-dihydropyrene.3To whom correspondence should be addressed.to achieve conjugation in the macro-ring of 1.

The barrier to rotation in 2,2″-dimethyl-o-terphenyl and several 3,3″-derivatives (rotational isomers of 1,2-di-o-tolylbenzene)

“…A // \ Syntheses Because of our interest in benzannelated annulenes (8) we required the bis-bromomethyl-oterphenyl 5. This was synthesized as follows.…”

Synthesis and Diatropicity of trans-2‘,5‘,10b,10c-Tetramethylfurano[3,4-e]-10b,10c-dihydropyrene. A Valence Isomerization To Form a Novel Isoannulenofuran at the Expense of Two Benzene and One Furan Rings

“…An obvious explanation is a significantly lower diatropicity (aromaticity) of the isoannelated compound 14b (internal methyl protons at δ 0.63). Assuming that proton shielding is proportional to ring current, 14b exhibits only <7% of the ring current of 11 (δCH 3 = −4.25)a value about 10% lower than that of the [ a ]-ring annelated system 10 (δCH 3 = 0.13, 0.15). This we believe is associated with the steric interactions derived from the external methyl groups in 14b resulting in a deviation from planarity of its molecular periphery.…”

Synthesis and Diatropicity of trans-N-Cyclohexyl-2‘,5‘,10b,10c-tetramethyl- pyrrolo[3,4-e]-10b,10c-dihydropyrene. The First Example of an Iso[17]annulenopyrrole

“…N -Cyclohexyl-2,5-dimethyl-3,4-bis(3-cyano-2-methylphenyl)pyrrole (23). Recrystallization (benzene/ n -hexane) yielded colorless crystals of 23 (65%): mp 190−192 °C; 1 H NMR δ 7.0−7.45 (m, 6H), 4.04−4.13 (m, 1H), 2.19, 2.31 (s, ratio 1:1, total 6H), 2.03, 2.11 (s, ratio 1:1, total 6H), 1.95 (br s, 10H); IR (KBr) 2220 (C≡N) cm -1 ; MS m / z 407 (M + , 100), 325 (75), 310 (27). Anal.…”

“…N -Cyclohexyl-2,5-dimethyl-3,4-bis(3-formyl-2-methylphenyl)pyrrole (24). Chromatography (dichloromethane/ n -hexane (1:1)) on silica gel gave colorless crystals of 24 (89%): mp 162−164 °C; 1 H NMR 10.25, 10.21 (s, ratio 1:1, total 2H), 7.0−7.7 (m, 6H), 3.87−4.20 (m, 1H), 2.32, 2.46 (s, ratio 1:1, total 6H), 2.09, 2.12 (s, ratio 1:1, total 6H), 2.04 (br s, 10H); IR (KBr) 1685 (CO) cm -1 ; MS m / z 413 (M + , 100), 398 (12), 385 (23), 370 (13), 331 (13), 316 (12), 303 (16). Anal.…”

“…N -Cyclohexyl-2,5-dimethyl-3,4-bis[3-(hydroxymethyl)-2-methylphenyl]pyrrole (25). Recrystallization (benzene) afforded colorless crystals of 25 (76%): mp 112−114 °C; 1 H NMR δ 6.9−7.1 (m, 6H), 4.11−3.85 (m, 1H), 2.10 (s, 6H), 1.98, 2.03 (s, ratio 1:1, total 6H), 1.94 (br s, 10H), 1.63 (s, 2H); IR (KBr) 3450 (OH) cm -1 ; MS m / z 417 (M + , 100), 402 (10), 325 (12); M r calcd for C 28 H 35 NO 2 417.2668, found (MS) 417.2660.…”