Oxy-Claisen

Anionic oxy-Claisen rearrangement.2 The [3,3] Claisen rearrangement of en-olates of a-allyloxy ketones is markedly dependent on the nature of the metal hydride used, and to a less extent, the solvent. An example is the rearrangement of a-(allyloxy)propiophenone (1) to the a-hydroxy ketone 2. The rearrangement... 

Because of the relative inertness of functional groups other than alcohols to Dess-Martin conditions, a Dess-Martin oxidation is a good choice when an in situ reaction of the resulting aldehydes or ketones is desired. It is particularly common to use Dess-Martin periodinane in order to generate very reactive aldehydes or ketones that suffer in situ concerted reactions, such as Diels-Alder additions,67 oxy-Claisen reactions,68 pericyclic processes69 and concerted hydrogen shifts.70... 

The third reaction, the oxy-Claisen rearrangement is very exothermic as most Claisen rearrangements are. Once again we can place more confidence in the magnitude of the numbers because all the groups required are available in the data bank. 

In analogy with the oxy-Cope rearrangement, it has been called an anionic oxy-Claisen rearrangement. Like the anionic oxy-Cope reaction, this reaction shows a high sensitivity to the metal cation and solvent. The reaction rate is in the order K > Na > Li and THF > toluene. 

The enolate derived from 2-vinyl-6-acyldihydropyran S-c/i provides cyclooctadienone via anionic oxy-Claisen rearrangement (Scheme 11)7 ... 

Allyl aryl ethers undergo accelerated Claisen and [1,3] rearrangements in the presence of a mixture of trialkylalanes and water or aluminoxanes. The addition of stoichiometric quantities of water accelerates both the trimethylaluminum-mediated aromatic Claisen reaction and the chiral zirconocene-catalyzed asymmetric carboalumination of terminal alkenes. These two reactions occur in tandem and, after oxidative quenching of the intermediate trialkylalane, result in the selective formation of two new C-C bonds and one C-0 bond (Eq. 12.70).153 Antibodies have also been developed to catalyze Claisen154 and oxy-Cope155 rearrangements. 

Barriault developed a new pericyclic domino process for the synthesis of the bioactive diterpenoid vinigrol (4-262), which was isolated from Vtrgaria nigra [92]. The natural product possesses antihypertensive and anti-platelet-aggregating properties. 4-262 contains a unique tricyclo [4.4.4.04a8a]tetradecane framework, which could be obtained by a combination of an oxy-Cope, a Claisen and an ene reaction... 

Scheme 10.27. Microwave-assisted domino oxy-Cope/Claisen/ene reaction...

In a series of publications over the past few years, the group of Barriault has reported on microwave-assisted tandem oxy-Cope/Claisen/ene and closely related reactions [175-178], These pericyclic transformations typically proceed in a highly stereoselective fashion and can be exploited for the synthesis of complex natural products possessing decalin skeletons, such as the abietane diterpene wiedamannic... 

Scheme 6.84 Tandem oxy-Cope/Claisen/ene reactions and related transformations.

A remarkable example is the combination of three pericyclic reactions for the synthesis of decalin frameworks with quaternary centers by a tandem oxy-Cope-ene-Claisen reaction shown in 163 [539] (Scheme 1.72). 

The Cope, oxy-Cope, and anionic oxy-Cope rearrangements belong to the category of [3,3J-sigmatropic rearrangements. Since it is a concerted process, the arrow pushing here is only illustrative. Cf. Claisen rearrangement. 

C Anionic oxy-Cope rearrangement 4d Claisen rearrangement of allyl vinyl ethers... 

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