title: Indenylidene complexes of ruthenium: optimized synthesis, structure elucidation, and performance as catalysts for olefin metathesis--application to the synthesis of the ADE-ring system of nakadomarin A.
abstract: An optimized and large scale adaptable synthesis of the ruthenium phenylindenylidene complex 3 is described which employs commercially available diphenyl propargyl alcohol 5 as a stable and convenient carbene source. Previous ambiguities as to the actual structure of the complex have been ruled out by a full analysis of its NMR spectra. A series of applications to ring closing metathesis (RCM) reactions shows that complex 3 is as good as or even superior to the classical Grubbs carbene 1 in terms of yield, reaction rate, and tolerance towards polar functional groups. Complex 3 turns out to be the catalyst of choice for the synthesis of the enantiopure core segment 77 of the marine alkaloid nakadomarin A 60 comprising the ADE rings of this target. Together with a series of other examples, this particular application illustrates that catalyst 3 is particularly well suited for the cyclization of medium-sized rings by RCM. Other key steps en route to nakadomarin A are a highly selective intramolecular Michael addition setting the quaternary center at the juncture of the A and D rings and a Takai-Nozaki olefination of aldehyde 73 with CH2I2, Ti(OiPr)4 and activated zinc dust.
authors.affiliation: Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, Germany. fuerstner@mpi-muelheim.mpg.de
authors.forename: A
authors.initials: A
authors.lastname: Fürstner
authors.forename: O
authors.initials: O
authors.lastname: Guth
authors.forename: A
authors.initials: A
authors.lastname: Düffels
authors.forename: G
authors.initials: G
authors.lastname: Seidel
authors.forename: M
authors.initials: M
authors.lastname: Liebl
authors.forename: B
authors.initials: B
authors.lastname: Gabor
authors.forename: R
authors.initials: R
authors.lastname: Mynott