The Abnormal Behavior of an Atropisomer: 3,3′‐Dibromo‐1,1′‐difluoro‐2,2′‐binaphthyl Reacting with Alkyllithium Compounds

Abstract

Abstract1‐Fluoro‐2‐(triethylsilyl)naphthalene (1) and other 1‐fluoronaphthalenes bearing a metalation‐resistant substituent at the 2‐position proved to be totally inert toward base attack. 3‐Bromo‐1‐fluoronaphthalene (6), readily prepared from the 2‐bromo isomer 5 by deprotonation‐triggered heavy halogen migration, was converted into 3,3′‐dibromo‐1,1′‐difluoro‐2,2′‐binaphthyl (8) by consecutive treatment with lithium diisopropylamide, copper(II) bromide and nitrobenzene. The dilithiated intermediate generated from the atropisomer 8 by treatment with 2 equiv. of butyllithium reacted with a variety of electrophiles to afford products such as the diacid 12 or the bis(phosphanes) 14 and 15 in high yields. The latter compound was also obtained in a straightforward manner from (4‐fluoro‐2‐naphthyl)diphenylphosphane oxide (16). Unexpectedly, neither the 3,3′‐dibromobinaphthyl 8 nor its 3,3′‐diiodo analogue 18 were amenable to a unilateral but only to a double‐sided halogen/metal permutation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)