Bulletin of the Chemical Society of Japan p. 473 - 480 (1981)
Update date:2022-09-26
Topics:
Yamamoto, Gaku
Oki, Michinori
Stereodynamics of a variety of 9-(3,5-dimethylbenzyl)triptycene derivatives was studied.Atropisomerism about the bridgehead-to-methylene bond was realized in a triply peri-substituted derivative, 8,13-dichloro-1,4-dimethyl-9-(3,5-dimethylbenzyl)triptycene: the activation enthalpy for the ap--> +/-sc conversion was 26.4 kcal/mol.Barriers to rotation about the bridgehead-to-methylene bond in a variety of triply, doubly, and singly peri-substituted derivatives were obtained by DNMR method.DNMR behavior of the diastereotopic m-methyl groups in the benzyl moiety revealed the dual mechanisms of the methyl exchange process; rotation about the methylene-to-aryl bond by 180 deg without rotation about the bridgehead-to-methylene bond ("isolated rotation (IR)") and rotation about the methylene-to-aryl bond by 180 deg synchronous with rotation about the bridgehead-to-methylene bond by 120 deg ("gear motion (GM)").The GM process predominates in peri-unsubstituted derivatives, while the IR process predominates in triply peri-substituted ones.
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Doi:10.1039/P19810000672
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