Halide trapping of the Nazarov intermediate in strained polycyclic systems: a new interrupted Nazarov reaction

• Published in: Tetrahedron letters Vol. 46; no. 34; pp. 5629 - 5632
• Main Authors: White, Timothy D., West, F.G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 22-08-2005
• Subjects: Carbocation; Diastereoselective; Halide; Lewis acid; Nazarov cyclization; Lewis acid; Carbocation; Diastereoselective; Halide; Nazarov cyclization
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/j.tetlet.2005.06.101

Upon treatment with TiCl
4, various bridged bicyclic dienones underwent Nazarov electrocyclization and efficient chloride trapping of the resulting cyclopentenyl cation. By this process, up to four new stereocenters are created with high control.
1,4-Dien-3-ones encased within bridged bicyclic frameworks undergo efficient Nazarov electrocyclization upon treatment with TiCl
4, but the resulting cyclopentenyl cations are trapped by chloride in preference to deprotonation. In contrast to the usual eliminative pathway, which destroys one of the stereocenters formed during electrocyclization, this process preserves both new centers and generates an additional one at the site of chloride trapping. Examples involving skeletal rearrangements and other Lewis acids are also discussed.