Spirocyclic anion intermediate

They proposed that [l,4]-sulfanyl participation gave a [2.2.1] bicyclic sulfonium salt intermediate 10a. This could be captured by the chloride anion to give either 19 (by path a) or 20 (by path b) as outlined in Scheme 3. It should be noted that the usual [l,2]-sulfanyl participation, via spirocyclic sulfonium ion 21, would only give the unrearranged chloride 19. 

The octahedral hexacoordinate anion (28) is readily hydrolyzed by either acids or alcohols to the spirocycle (110) (Equation (23)). Chiral systems, which are prepared by fractional crystallization of the methyl Brucinium diastereomers, give optically inactive systems on ring cleavage <67LA(705)66>. Octahedral anionic species similar to (46) have been proposed as intermediates in nucleophilic substitution reactions at arsenic <72PS(2)129> (see Section 2.16.9.1). 

The palladium-catalyzed cleavage of an allylic C-C bond forming cationic )t-allylpalladium intermediates is possible if the anionic counterpart is stabilized through charge delocalization on electron-deficient substituents [29]. Based on this concept, it has been shown that 3-vinylcyclopentenes undergo a two-carbon ring expansion to spirocyclic cyclopheptadienes in the presence of... 

Our synthesis commenced with metalating iodide 414, and addition of the ensuing alkyllithium to the enantiomeri-cally pure (5)-lactam 413 provided the ring-opened, Boc-protected amino ketone 412 in 61% yield (Scheme 12.104). A formic acid-induced aza-Prins cyclization afforded an inseparable diastereomeric mixture of aza-spirocycles 415 in which the allyl cation intermediate had been trapped by the formate anion. 

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