定义Definition
频哪醇重排是邻二醇在酸催化下失水并发生 1,2-迁移，生成醛或酮的反应；典型例子是频哪醇（2,3-二甲基-2,3-丁二醇）重排为频哪酮（3,3-二甲基-2-丁酮）。
The pinacol rearrangement converts a 1,2-diol under acid catalysis, with loss of water and a 1,2-shift, into an aldehyde or ketone; the classic case is pinacol (2,3-dimethylbutane-2,3-diol) to pinacolone (3,3-dimethylbutan-2-one).
机理Mechanism
一个羟基质子化后失水，生成较稳定的碳正离子；相邻碳上的一个基团带着电子对 1,2-迁移到正电荷中心，产生的新正离子被相邻氧的孤对电子稳定（氧鎓离子），失去质子得羰基化合物。
One hydroxyl is protonated and leaves as water, giving the more stable carbocation; a group on the neighbouring carbon shifts with its electrons, and the new cation, stabilised by the oxygen lone pair (oxocarbenium), loses a proton to give the carbonyl.
选择性Selectivity
先离去的是能生成更稳定碳正离子的那个羟基；迁移能力一般为 H、芳基 > 烷基（富电子芳基迁移更快）。半频哪醇重排（如 β-卤代醇、环氧化物开环）原理相同，可用于扩环、构建季碳中心。
The hydroxyl that gives the more stable cation leaves first; migratory aptitude is generally H, aryl > alkyl (electron-rich aryls fastest). Semipinacol variants (halohydrins, epoxide opening) use the same principle for ring expansions and quaternary centres.
由来Origin
鲁道夫·菲蒂希于 1860 年首先描述，但当时未能正确解释产物结构，后来才被阐明。
First described by Rudolph Fittig in 1860, though the product structure was only explained correctly later.
反应Reactions
稀硫酸或其他质子酸、路易斯酸，加热
Dilute sulfuric acid or other protic or Lewis acids with heating
羟基质子化失水生成碳正离子。
Protonation and loss of water give a carbocation.
邻位甲基 1,2-迁移。
A neighbouring methyl undergoes a 1,2-shift.
氧鎓离子失去质子得酮。
The oxocarbenium ion loses a proton to the ketone.
经典例子。
The classic example.
反应机理图Mechanism
红色弯箭头表示一对电子的移动方向：从电子来源（孤对电子或化学键）指向电子去向。Red curly arrows show where an electron pair moves: from its source (lone pair or bond) to its destination.
一个羟基质子化
One OH is protonated
失水生成叔碳正离子
Water leaves, giving a tertiary carbocation
甲基 1,2-迁移，正电荷落到有 OH 的碳上并被氧稳定
A methyl shifts (1,2); the cation lands on the C–OH carbon, stabilised by O
质子化的酮
Protonated ketone
频哪酮
Pinacolone
年表Timeline
- 1860
菲蒂希报道频哪醇转化
Fittig reports the pinacol transformation