US EPA

8313608 

Journal Article 

Toward the Understanding of Benzannelated Annulenes: Synthesis and Properties of an [e]-Ring Monobenzannelated Dihydropyrene 

Mitchell, RH; Yan, JSH; Dingle, TW 

1982 

Yes 

Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 

AMER CHEMICAL SOC 

WASHINGTON 

104 

9 

2551-2559 

English 

10.1021/ja00373a037 

WOS:A1982NN22100037 

The benzo[e]-annelated dimethyldihydropyrene 2 was synthesized in 9.9% yield in nine steps from o-dibromobenzene by using either a Wittig rearrangement-Hofmann elimination sequence on the benzo[3.2]thiametacyclophane 9 or, alternatively, a benzyne-induced Stevens rearrangement of 9 followed by oxidation to the sulfone 22 and then base catalyzed sulfinate elimination to 2. The benzannulene 2 was shown to undergo electrophilic substitution reactions (nitration, acylation) and reversible photoisomerization with the cyclophanediene 8. The rate of this isomerization was slower than that for the nonbenzannelated 6. Methylation of the sulfone 22 provided a novel entry to the bridge-substituted derivative 4-methyl-2 and also to a cyclophane with an exo methylene group on the bridge, 36. The shielding of the internal protons of 2 is discussed in terms of bond localization, as are the observed coupling constants for its external protons. The 1H NMR spectrum is compared to that of benzo[e]pyrene, and the analysis supports Gϼnther's hypothesis that cofusion of the two rings results in considerable bond localization in each. The coupling constant analysis also indicates that the benzo ring localizes the 14π ring more than vice versa. © 1982, American Chemical Society. All rights reserved.