Claisen rearrangements of allyl vinyl ether

Scheme 6.14. Claisen Rearrangements of Allyl Vinyl Ethers and Related... 

As shown earlier in many examples, the Claisen rearrangement of allyl vinyl ethers also provides a very powerful method for carbon-carbon bond formation in domino processes. Usually, the necessary ethers are formed in a separate step. However, both steps can be combined in a novel domino reaction developed by Buchwald and Nordmann [306]. This starts from an allylic alcohol 6/4-102 and a vinyl iodide 6/4-103, using copper iodide in the presence of the ligand 6/4-104 at 120 °C to give 6/4-105 (Scheme 6/4.25). The reaction even allows the stereoselective formation of two adjacent quaternary stereogenic centers in high yield. 

The Claisen rearrangement of allyl vinyl ether in aqueous solution was studied by Gao et al. [157] by using the gas-phase ab initio MEP determined previously by the Jorgensen s group [60], In this case, 69 of the 143 frames were employed along the perturbation procedure in the isothermal-isobaric ensemble at 25 °C and 1 atm. The... 

Gao, J. Combined QM/MM simulation study of the Claisen rearrangement of allyl vinyl ether in aqueous solution, JAm.Chem.Soc., 116(1994), 1563-1564... 

Davidson, M. M., Hillier, I. El., Hall, R. J. and Burton, N. A. Effect of solvent on the Claisen rearrangement of allyl vinyl ether using ab initio continuum methods, J.Am.Chem.Soc., 116 (1994), 9294-9297... 

Severance, D. L. and Jorgensen, W. L. (1994) Claisen rearrangement of allyl vinyl ether,in Cramer, C. J. and Truhlar, D. G.(eds.), Structure and Reactivity in Aqueous Solution, American Chemical Society, Washington, pp.243-259. 

Sattelkau and Eilbracht90 have exploited the Claisen rearrangement of allyl vinyl ethers in their synthesis of several spiro compounds. As shown below in equation 62, 7,9-dimethyl-l,4-dioxa-spiro[4,5]decan-8-one, 118, was converted to a ,/J-unsaturated ester 119 which was reduced to allyl alcohol 120906. Allyl vinyl ether 121 underwent a rhodium-catalyzed Claisen rearrangement to afford 7r,13r-dimethyl-l,4-dioxa-(8rC9)-dispiro[4.2.4.2]tetradecan-10-one (122) in 36% yield. 

The Claisen rearrangement of allyl vinyl ethers is a classic method for the stereoselective synthesis of y,J-unsaturated esters. The allylic C-H activation is an alternative way of generating the same products [135]. Reactions with silyl-substituted cyclohexenes 197 demonstrate how the diastereoselectivity in the formation of 198 improves (40% to 88% de) for the C-H insertion reactions as the size of the silyl group increases (TMS to TBDPS) (Tab. 14.14). Indeed, in cases where there is good size differentiation between the two substituents at a methylene site, high diastereo- and enantioselectivity is possible in the C-H activation. 

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

The procedure described illustrates a new general synthetic method for the preparation of (E)-3-allyloxyacryl ic acids and their conversion to a-unsubstituted y,5-unsaturated aldehydes by subsequent Claisen rearrangement-decarboxyl at ion. Such aldehydes are traditionally prepared by Claisen rearrangements of allyl vinyl ethers. Allyl vinyl ethers are typically prepared by either mercury-catalyzed vinyl ether exchange with allylic alcohols or acid-catalyzed vinylation of allylic alcohols with acetals. The basic conditions required for alkoxide addition to the betaine to produce carboxyvinyl allyl ethers, as described in this report, nicely complements these two methods. In addition, this Claisen rearrangement is an... 

Figure 11.5 Gas-phase reaction coordinate for the Claisen rearrangement of allyl vinyl ether...

The Cope and Claisen rearrangements are markedly similar reactions, although they differ in thermodynamic driving force. Whereas the Cope rearrangement of 1,5-hexadiene is thermoneutral (reactant and product are the same), the analogous Claisen rearrangement of allyl vinyl ether is exothermic. Do thermodynamic differences lead to differences in transition state geometries ... 

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. 

Only few investigations concerning the Claisen rearrangement of allyl vinyl ether bearing an amino substituent on C(1)92-94, C(5)95,96 and C(6)97 have been reported. 

It can be seen from the examples displayed above that the Claisen rearrangement of allyl vinyl ethers with an amino substituent at C(n and C(2) proceeds much faster than that of allyl vinyl ether itself. Several models98- 00 have been proposed in order to interpret the substituent effect on the rate of Claisen rearrangement. Both the acceleration of the rearrangements of / -allyloxyenamine and 0-allylketene TV, 0-acetals and deceleration of the reaction of enamine 120 are in agreement with the prediction of the models. 

Claisen rearrangement of allyl vinyl ethers. " Allyl vinyl ethers undergo Claisen rearrangement at 25° in CICHiCHiCl in the presence of 2 equiv. of (CjH liAlSQH, (prepared from triethylaluminum and thiophenol) or (C3H5)2AICI/P(CftH,),. 

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). 

The Claisen rearrangements of allyl vinyl ethers yield y, 8-unsaturated carbonyl compounds. When R = NR2 the rearrangement is known as the Eschenmoser-Claisen... 

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