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An Efficient Synthetic Approach to Substituted Penta‐ and Hexahelicenes
Author(s) -
Minuti Lucio,
Taticchi Aldo,
Marrocchi Assunta,
GacsBaitz Eszter,
Galeazzi Roberta
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199911)1999:11<3155::aid-ejoc3155>3.0.co;2-s
Subject(s) - racemization , aromatization , chemistry , nuclear magnetic resonance spectroscopy , computational chemistry , stereochemistry , organic chemistry , catalysis
A two‐step synthetic approach to penta‐ and hexahelicenes substituted at the terminal aromatic rings has been studied. This approach is based on the Diels–Alder reaction of 5,5′,8,8′‐tetramethyl‐3,3′,4,4′‐tetrahydro‐[1,1′]‐binaphthalene (2b) , 3‐vinyl‐1,2‐dihydronaphthalene (5a) , 5,8‐dimethyl‐3‐vinyl‐1,2‐dihydronaphthalene (5b) and 3‐vinyl‐1,2‐dihydrophenanthrene (15) followed by the aromatization of the cycloadducts. This method is flexible, efficient and of wide application to the synthesis of several benzenoid and nonbenzenoid penta‐ and hexahelicenes. The racemization energy barriers of helicenes 3 , 9 , 10 , 13 , 14 , 17 and 18 were computed with the semiempirical quantum method AM1. The computed values show that, when methyl groups are introduced at the inner position of the terminal aromatic rings, the racemization barriers increase markedly. A structure analysis of the reaction products by 1 H‐ and 13 C‐NMR spectroscopy is also presented.