[formula: see text] The coupling of o-alkynylbenzoyl derivatives with carbene complexes has been investigated. The reaction initially affords isobenzofuran derivatives, which convert to alkylidenephthalan derivatives or can be trapped by various dienophiles to afford benzo-oxanorbornene derivatives.
A stereoselective synthetic approach to spirooxindole γ-butyrolactams is developed via N-heterocyclic carbene-catalyzed formal [3 + 2] annulation of α-bromoenals with 3-aminooxindoles. An enantioselective variant of this methodology is also investigated resulting in good substrate tolerance and high enantioselectivities.
[reaction: see text] The synthesis of isoquinolines through coupling of 2-alkynylbenzaldehyde derivatives with beta-cyanocarbene complexes has been examined. The reaction involves formation of an isobenzofuran followed by intramolecular Diels-Alder reaction with the nitrile, a process with limited precedent. The unique success of this process in this system has been attributed to deoxygenation of the initial adduct to form the isoquinoline ring system.
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