Vinyl ethers thermal rearrangement

Claisen rearrangement of allyl vinyl ethers. Thermal rearrangement of vinyl ethers (3) of sec-allylic alcohols in the presence of 1 or 2 leads to the aldehyde 4. Rearrangement of the optically active 5 is accompanied by transfer of chirality, particularly in the case of 1. 

A number of vinylation-Claisen rearrangements have been reported as a tandem reaction. Since no additional reagents are required in the thermal Claisen rearrangement, the allyl vinyl ethers can rearrange without isolation. No convenient introduction methods of basically reactive vinyl groups are available for the selective preparation of functionalized vinyl ethers [11,13,14, 22, 24]. 

The Claisen rearrangemenC is a thermal rearrangement of allyl aryl ethers and allyl vinyl ethers respectively. It may be regarded as the oxa-version of the closely related Cope rearrangement. Claisen has discovered this reaction first on allyl vinyl ethers 1, and then extended to the rearrangement of allyl aryl ethers 2 to yield o-allylphenols 3 ... 

This flask must be cleaned with h ot chromic acid solution and then, along with all other glassware used in this preparation, soaked in a base solution, rinsed with distilled waiter, and oven dried. Thermal rearrangement of the intermediate vinyl ether in a new (untreated) flask resulted in elimination. 

So basically the Claisen rearrangement is a thermal [3, 3] sigmatropic rearrangement of allyl vinyl ether. The mechanism is probably as follows ... 

Sheradsky has found that the hydroxyl function of a ketoxime such as acetophenone oxime can be made to react with DMAD when the reaction is carried out in methanol with a basic catalyst, to give mixture of the fumarate and maleate isomers (164) in the ratio 2 1. This mixture on heating undergoes a hetero-Cope rearrangement followed by cyclization and dehydration to give dimethyl 5-phenylpyrrole-2,3-dicarboxylate (168) (Scheme 25). Similarly, Heindel and Chun have reported that vinyl ether adducts (171), obtained by the condensation of arylamide oximes with DMAD, get thermally converted into oxa-diazolines (172) or imidazolinones (174), depending on the reaction conditions. A similar reaction occurs with aromatic amidoxime-methyl propiolate adducts to give imidazoles (170) (Scheme 26). 1,2,4-Dioxazoles have been reported to be formed in the reaction of hydrox-amic acids with DMAD. - ... 

Thermal propargyl rearrangement-Claisen rearrangement of propargyl vinyl ethers and Cope-type rearrangements of propargyl malonates [93]. 

PdCl2(PhCN)2-catalysed Claisen rearrangement of the allyl vinyl ether 474 derived from cyclic ketone at room temperature affords the syn product 475 with high diastereoselectivity [203]. In contrast to thermal Claisen rearrangement, the Pd(II)-catalysed Claisen rearrangement is always stereoselective, irrespective of the geometry of allylic alkenes. The anti product is obtained by the thermal rearrangement in the presence of 2,6-dimethylphenol at 100 °C for lOh. 

The aliphatic Claisen Rearrangement is a [3,3]-sigmatropic rearrangement in which an allyl vinyl ether is converted thermally to an unsaturated carbonyl compound. 

Claisen rearrangement (Sections 18.4 and 30.8) the thermal [3.3] sigmatropic rearrangement of an allyl vinyl ether or an allyl phenyl ether. 

Anionic Claisen rearrangement. Acceleration of the Claisen rearrangement of allyl vinyl ethers was originally observed with potassium hydride in HMPT, but even milder conditions are possible using sodium or lithium dimsylate. The catalyzed rearrangement is as stereoselective as the thermal counterpart. Thus vicinal asymmetric centers are formed selectively on rearrangement of (E)- and (Z)-crotyl ethers (equations I and II). 

A mercury-free route to allyl vinyl ethers that relies on the Michael addition of allyl alcohols to unsubstituted alkenyl sulfoxides, followed by thermal loss of sulfenic acid and concurrent Claisen rearrangement has been described [145]. This methodology has been applied to the synthesis of isocar-bacyclin [146]. Posner reported an acid-catalyzed protocol that produces conjugated dienoate esters from allylic alcohols and a sulfinyl orthoester [147]. Additionally, the use of propargyl alcoholates and a chloro alkenyl sulfox-... 

The uncatalyzed traditional Claisen rearrangement of allyl vinyl ethers is still very much in use, especially for the preparation of quaternary centers of carbocyclic systems. The rearrangement is highly exothermic, but generally requires temperatures of 150-200 C and is therefore limited to thermally stable compounds. 

The thermal [3,3]-sigmatropic rearrangement of allyl vinyl ethers, first reported by Claisen in 1912, allows the preparation of y,6-unsaturated carbonyl compounds. This reaction is called [3,3]-sigmatropic rearrangement because the new a-bond has a 3,3 relationship to the former a-bond. The aromatic variant of the Claisen rearrangement, in which an aryl allyl ether (5) is converted thermally to the corresponding y,6-unsaturated carbonyl compound (6), is followed by a re-aromatization providing an ortho-di y phenol (7). 

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