Reversal of the regiochemistry in the rhodium-catalyzed [4+3] cycloaddition between vinyldiazoacetates and dienes
A regio-, diastereo-, and enantioselective [4+3] cycloaddition between vinylcarbenes and dienes has been achieved using the dirhodium tetracarboxylate catalyst [Rh2(SBTPCP)4]. This methodology provides facile access to 1,4-cycloheptadienes that are regioisomers of those formed from the tandem cyclopropanation/Cope rearrangement reaction of vinylcarbenes with dienes.
A new approach to the Nazarov reaction via sequential electrocyclic ring opening and ring closure
Regioselective dichlorocyclopropanation of 2-silyloxydienes furnishes vinylcyclopropanol silyl ethers in good yield. Treatment with silver(I) at room temperature effects disrotatory electrocyclic opening to a 2-chloro-3-silyloxypentadienyl cation, which then undergoes conrotatory (Nazarov) electrocyclization to provide chlorocyclopentenones. This two-step sequence offers a convenient and mild alternative to the standard Nazarov cyclization protocol via a formal 4+1 construction and furnishes products containing useful halogen functionality. In one case possessing a pendant phenyl group, interrupted Nazarov reaction to give a benzohydrindenone was observed. Copyright
Grant, Tina N.,West
p. 9348 - 9349
(2007/10/03)
Diastereoselektive sequentielle Umsetzung von Benzothiopyrylium-Salzen zu anellierten Benzothiopyranonen