Direct access to substituted brendane derivatives by palladium-copper mediated cyclisation of endo-5-vinyl-2-norbornene. X-ray structure of the σ-π intermediate palladium complex. Further evolution (Baeyer-Villiger oxidation) to the quinane system

Abstract

A one-step synthesis of disubstituted brendane derivatives is described starting from (commercially) available vinyl norbornene by the Wacker-type oxidation with PdCl 2/CuCl 2 or PdCl 2/CuCl n/O 2 (n=1,2). In addition to the formation of a new carbon carbon bond two different nucleophilic groups are incorporated with complete chemio-, regio- and high (>90%) stereoselectivity. The NMR and X-Ray structure analysis of a σ-π-palladium-bipyridine complex clearly establishes the stereochemistry of the prerogative intermediate and the position of the coordinated vinyl group in an ‘extracyclic’ position before the insertion-cyclisation step. This stereochemistry establishes the oxidative cleavage of the cyclised ( cis-insertion) organopalladium intermediate to proceed with predominant (90%) inversion of configuration. A further ring opening reaction via Baeyer-Villiger oxidation has been developed showing the usefullness of the brendane derivatives for an easy access to functionalized quinane system(s) with complete stereocontrol of 5 stereogenic centers.