Bis(pentamethylcyclopentadienyl)keton und ‐thioketon: Kohlenstoff‐Verbindungen mit präformierter Diels‐Alder‐Geometrie

Abstract

Bis(pentamethylcyclopentadienyl) Ketone and Thioketone: Carbon Compounds with Performed Diels‐Alder Geometry1,2,3,4,5‐Pentamethyl‐1,3‐cyclopentadien‐5‐carbonyl chloride (2) is formed in good yields by the reaction of pentamethylcyclopentadienyllithium (1) with phosgene. The corresponding carbothioyl chloride 3 is synthesized by treatment of 1 with thiophosgene. Both acyl chlorides are stable against air and moisture and difficult to attack in SN2‐type reactions. Treatment of 2 and 3 with trimethyl(pentamethylcyclopentadienyl)stannane in the presence of boron trifluoride — ether leads to bis(1,2,3,4,5‐pentamethyl‐1,3‐cyclopentadien‐5‐yl) ketone (5) and thioketone (6), respectively. Even at room temperature, 5 and 6 tend to intramolecular [4 + 2] cycloaddition reactions. X‐ray crystal structure investigations of 2, 5, and 6 show the steric demand of the pentamethylcyclopentadienyl ligand and explain the untypical chemical behavior of 2 and the easy [2 + 4] cycloaddition reactions of 5 and 6.