Synthetic and Theoretical Investigations on the Construction of Oxanorbornenes by a Michael Addition and Intramolecular Diels–Alder Furan Reaction

Abstract

The conjugate addition of nucleophiles such as allylmercaptan, allyl‐ and homoallylmalonate and diallylamine to β‐furyl enones and acrylate, provides the Michael adducts in good yield. A facile intramolecular Diels–Alder reaction between the unsaturated tether and the furan diene ensues when these adducts are heated in a solvent such as toluene orxylene to afford the cycloadducts in good yield and excellent stereoselectivity in most cases. The structure and stereochemistry of these cycloadducts were confirmed by extensive NMR experiments and X‐ray crystallography. Quantum chemical calculations on the transition state and product geometries suggest that the formation of the cycloadducts, in which the newly formed ring is exo‐fused to the oxanorbornene framework, is favored over the endo‐fused product due to less strain in the former and its transition state.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Scope of Stereoselective Mn-Mediated Radical Addition to Chiral Hydrazones and Application in a Formal Synthesis of Quinine

“…The concept of torsional steering was introduced by Houk to explain selectivities in additions to alkenes and carbonyl compounds: transition states that have a forming σ bond in a staggered conformation are stabilized relative to eclipsed transition states . This concept has been used to rationalize unexpected selectivities in epoxidations or cycloadditions from more sterically hindered faces of alkenes. In the context of the cyclization of 42 , TS-A has a number of bonds eclipsed (Figure ), while several of these same bonds are in staggered conformations in TS-B and TS-C .…”

Synthesis of hydronaphthalenes through coupling of enyne-carbonyl compounds that contain pendant alkane groups with Fischer carbene complexes

“…Most of the high-yielding reactions involve activated systems such as electron-deficient alkenes,4 allenes,5 or a favorable gem dialkyl effect 6. Six-membered ring forming intramolecular furan Diels-Alder reactions involving unactivated alkenes are often low-yielding,7 although several high-yielding processes have been reported 8. The net transformation is a unique construction of a hydronaphthalene9 from two five-carbon pieces where both components contribute at least one carbon to both of the newly-formed rings.…”