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Stereoselective Synthesis of Spirocyclic Ketones by Nazarov Reaction

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journal contribution
posted on 29.09.2005, 00:00 by Cristina Prandi, Annamaria Deagostino, Paolo Venturello, Ernesto G. Occhiato
The Suzuki−Miyaura cross-coupling reaction between α-ethoxydienyl boronates and lactone-derived vinyl triflates affords functionalized 6-(1-ethoxy-1,3-butadienyl)dihydropyran derivatives that undergo a Nazarov electrocyclic reaction under mild acidic conditions to give functionalized spirocyclic ketones. The product distribution and the stereoselectivity of the process are strongly dependent on the substitution of both the α-ethoxydiene and dihydropyran moieties. High stereoselectivity is observed in the presence of a C2-substituent on the dihydropyran moiety. The results are explained in terms of transition state geometries.