Stereoselective Synthesis of Bicyclo[4.2.1]nonane Skeletons by Ring-Closing Metathesis:  A New Versatile Methodology for the Efficient Assembly of Functionalized Cyclooctanoids

Abstract

[reaction: see text] A new versatile methodology, resulting in a formal three-carbon ring expansion of cyclopentanones, for the efficient assembly of functionalized cyclooctanoids is described. The approach is based on the chemo-, regio-, and stereoselective alpha,gamma-difunctionalization of beta-ketoesters followed by ring-closing metathesis to form functionalized bicyclo[4.2.1]nonanes, precursors of the corresponding cyclooctanes, by selective ring cleavage of the one-carbon-atom bridge.

Selective Construction of Carbocyclic Eight‐Membered Rings by Ring‐Closing Metathesis of Acyclic Precursors

“…Mascareaeas and co-workers [78] introduced the selective formation/fragmentation of bicyclo-[3.3.1]nonanones with a hydroxy group at the bridgehead (Scheme 40). These intermediates were obtained in very good yields by RCM of an a-vinyl-a'-allyl-(shown in Scheme 40) or a-vinyl-a'propargylhydroxycyclohexanone using only [79] The required doubly unsaturated precursors were obtained through a domino process involving chemo-, regio-, and stereoselective a,g-difunctionalization of a bicyclic b-ketoester. This crucial transformation takes advantage of the specific structure of the starting bicyclo[3.3.0]octane, which allows very good control over the required 1,3-cis arrangement of the two unsaturated chains.…”

Construction of Eight-Membered Carbocycles with Trisubstituted Double Bonds Using the Ring Closing Metathesis Reaction

“…Further applications involving cyclization to cycloheptene derivative 4 6 and the ring opening to cyclooctene 47 was realized by Rodriguez ( Scheme 10 ) [ 28 , 29 ]. An interesting review was published by Rodriguez [ 30 ].…”

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“…Schließlich führten wir kürzlich eine stereoselektive RCM‐Synthese von Bicyclo[4.2.1]nonan‐Gerüsten ein, die mit einem Pentacyclus anelliert sind (Schema ). Es handelt sich um eine neue, vielseitige Methode für den effizienten Aufbau funktionalisierter Cyclooctanoide in Naturstoffen 79. Die erforderlichen zweifach ungesättigten Vorstufen wurden aus einem Dominoprozess erhalten, der eine chemo‐, regio‐ und stereoselektive α,γ‐Difunktionalisierung eines bicyclischen β‐Ketoesters umfasst.…”