Catalytic Hydrolithiation of Guaiazulene: Isolation of Two Isomerically Pure Renewable Feedstock‐Based Cyclopentadienyl Synthons

Abstract

AbstractWe present an in‐depth study of hydride transfer or proton abstraction at natural product guaiazulene to form guaiazulenide salts (8‐H‐GuaH)Li 1 a and (Gua’’)Na(OEt2) 2. Both carbanions were correctly proposed by Hafner et al. but could never be isolated in isomerically, spectroscopically and analytically pure form so far. Therefore, their use as cyclopentadienyl synthons in organometallic chemistry remained essentially unexplored. Here, we present their synthesis and full characterisation including 2D NMR spectroscopy and two XRD structural analyses. 1 a is isolated in isomerically and chemically pure form via a catalytic variant of olefin hydrolithiation, the addition of LiH to an activated hydrocarbon C=C double bond catalysed by LiAlH4. This atom economic synthesis of a pure organolithium compound from an olefin, LiH or lithium and dihydrogen, respectively, is without precedence. In a follow up report we will demonstrate that these valuable ligand salts can be used as cheap sterically demanding renewable feedstock‐based cyclopentadienyl synthons in the synthesis of homo‐ and heteroleptic late transition metal complexes and catalysts.