Reaction of quinidine acetate, epiquinidine and its acetate in superacid: formation of gem-difluoro derivatives with or without rearrangement

Molecular Rearrangements: Part 2. Other Reactions

“…The Lewis acid-promoted rearrangement of 2,2,3,3-tetrasubstituted de 2,3-epoxyalcohol derivatives, which have only a slight difference in stability of carbocation at the C(2) or C(3) positions, proceeds through the C(3) carbocation. Monitoring by 1 H NMR suggested the (−)-isocomene (64) as an intermediate, further proved by transformation ee of natural (64) to (63 A selective high-yielding (90%) acid-catalysed ring contraction of 1-benzyl-2methyl-3-piperidone (65) to 1-benzyl-2-acetylpyrrolidine (66) occurs by refluxing in 6 m HCl for 24 h (Scheme 19). 48 The semi-pinacol rearrangement of alkenyl-substituted 2,3-epoxycyclopentanols gives stereoselectively α-alkenylated cyclopentanones.…”

“…It should be noted that the pinacol-type epoxide ring rearrangement gives in this case the β-methyl that is anomalous according to the attack of the hydride of the leaving C-O bond from the back side. 64 55 The rearrangement involved protonation, 1,2 s-bond and methyl shifts, and deprotonation.…”

Quinoline, quinazoline and acridonealkaloids

“…Various cyclised, rearranged and fluorinated products have been isolated from the reaction of quinidine, epiquinidine 104 and their acetates in the hydrofluoric acid-antimony pentafluoride superacidic medium. 43 The chiral amine 105 has been prepared from (−)-quinine 97 by a lengthy reaction sequence. 44 This product was designed as a pseudoenantiomer of b-isocupreidine 106, available in a single step from quinidine, which is a useful chiral catalyst for asymmetric Baylis-Hillman reactions of hexafluoroisopropyl acrylate.…”

Superacid‐Catalyzed Reactions

“…549 The pathway given in Scheme 5.56 can also explain the formation of these products. 549 The pathway given in Scheme 5.56 can also explain the formation of these products.…”