Payne rearrangement equilibrium

It is appropriate at this juncture to address some of the more useful transformations of 2,3-epoxy alcohols.913 A 2,3-epoxy alcohol such as compound 14 possesses two obvious electrophilic sites one at C-2, and the other at C-3. But in addition, C-l of a 2,3-epoxy alcohol also has latent electrophilic reactivity. For example, exposure of 14 to aqueous sodium hydroxide solution results in the formation of triol 19 in 79% yield (see Scheme 5). In this interesting transformation, hydroxide ion induces the establishment of an equilibrium between 2,3-epoxy-l-ol 14 and the isomeric 1,2-epoxy-3-ol 18. This reversible, base-induced epoxide migration reaction is a process known as the Payne rearrangement.14... 

Epoxy-3-alcohols can be derived from 2,3-epoxy-1-alcohols by the base-catalyzed Payne rearrangement as illustrated in step d of Figure 6A.4 [59,64], The rearrangement is completely stereospecific but, because it is reversible, it usually results in an equilibrium mixture of the two epoxy alcohols for which the relative proportions are structure-dependent. Practical synthetic applications of this rearrangement therefore depend on methods that will shift the equilibrium completely in the direction desired. Nucleophiles such as thiolates and amines are... 

A key reaction of 2,3-epoxy alcohols is the Payne rearrangement, an isomerization that produces an equilibrium mixture. This rearrangement then allows for the selective reaction with a nucleophile at the most reactive, primary position (Scheme 9.5).18,84... 

In view of the excessive length of the 10-step preparation of the substrate 30 from 19, we planned to develop a more convenient route to 30. Our improved route is depicted in Scheme 4. The Payne rearrangement of 19 with KN(TMS)2 in the presence of 18-crown-6 ether in THF at -18 °C afforded the epoxy-migrated compound 20 in 62% yield along with 30% recovery of 19. This Payne rearrangement produced the equilibrium mixture of 20 and 19. We explored this rearrangement by changing the base and reaction temperature. The most... 

Scheme 8.11 Payne-like opening of epichloro-hydrin during syntheses of aryloxypropanola-mine beta-blockers. Pathway A shows a true Payne rearrangement [178] as it pertains to how a 2,3-epoxy alcohol becomes isomerized when treated with aqueous base. Step 1 is meant to show how the initial intermediate alkoxide first attacks the 2-position to cause an inversion of stereochemistry. Since the same process can then be repeated from the other direction (step 2), an equilibrium is eventually obtained where the preponderance of one isomer over the other is dictated by whatever other substituents may be present.

On alkaline treatment of the 3,3-dimethyl glycidol, Payne rearrangement takes place. In alkaline aqueous solutions, 2,3-epoxy alcohols are in equilibrium with the corresponding 1,2-epoxy alcohols. Payne was the first to observe this... 

Y-Amino-acids. - A total synthesis of the amino-acid (514), a component of the anti-tumour antibiotic carzinophilin, features a one-pot Payne rearrangement-azide opening of the chiral epoxide (512) in which the use of phase-transfer conditions is crucial to force the equilibrium over to the primary azideadduct (513). ... 

The isomerization of 2,3-epoxy alcohol 1 under the influence of a base to l,2-epoxy-3-ol 2 is referred to as Payne rearrangement. It involves an equilibrium of the epoxy alcohol 1 with the isomeric 2 and the reaction is stereospecific, proceeding with inversion of configuration at C-2 carbon of the epoxide ring via Sn2 t5q>e mechanism. 

The mechanism of Payne rearrangement involves intramolecular nucleophilic attack by an alkoxide on an adjacent epoxide to form an isomeric alkoxide. This isomerisation results an equilibrium mixture of the two epoxides, the position of which is controlled by the relative thermodynamic stabilities of the two compounds. 

Payne further investigated the scope and limitations of the epoxy alcohol rearrangement under the standard conditions depicted in Scheme 10.1. A major quantity of 3 was found to be readily transformed to the isomeric 4, attaining an equilibrium ratio of 3 4 = 8 92. The position of equilibrium for this structural transposition was further probed by using representative isomeric substrates thus, only a small amount of anti-6 was obtained from (E)-5, while the diastereomeric syn-6 was formed from (Z)-5 as a mixture of syn-6 (Z)-5 = 42 58 after 1 h at ambient temperature. The same situation was noticed for (E)-7, which afforded anti-S in a ratio of E)-7 anti-6 = 44 56, and (Z)-7, which was preferentially converted to syn-8, leaving only 5% of (Z)-7 in the mixture. 

---