Electrophilic substitution with allylic rearrangement (SE′) stereochemistry of trifluoroacetolysis of some cyclohex-2-enylmetal compounds

Article abstract of DOI:10.1021/om00095a027

A range of (4-alkylcyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)silanes, (4-alkylcyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)germanes, and (4-alkyl-cyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)stannanes were cleaved to the cycloalkene (and R₃MX) with trifluoroacetic acid-d in various solvents. Complete allylic rearrangement (γ-attack) was observed, and the preferred direction of delivery of the electrophile (formally D⁺) to the γ-carbon of the allylic triad was determined by detailed ¹H, ¹³C, and ²H NMR analyses of the derived dibromides of the various alkyl-substituted cyclohexenes or by direct ²H NMR analysis and comparisons with ²H-substituted alkylcyclohexenes of established relative configurations. A highly preferred γ-anti mode of acidolysis is established for all systems, except for the trans-4-tert-butylcyclohex-2-enyl derivatives, such exception being ascribed to steric impedance of electrophile approach, promoting syn attack. Thus, overall, highly γ-regioselective and anti-stereoselective substitutions (S_E′) are observed.