The Claisen Rearrangement of Allyl Vinyl Ether

There have been two recent analyses of the hydration effeas on the Claisen rearrangements among previous studies, one using the SCRF AMI-SM2 model by Cramer and Truhlar, and the other employing Monte Carlo simulation with die OPLS potential by Severance and Jorgensen. The two methods are complementary to each other, in that the former calculation indudes the molecular electronic polarization whereas the latter treats solute-solvent intermolecular interactions explicidy. Cramer and Truhlar reported a rate acceleration of 21-fold, or a AAGl j of —1.6 kcal/mol, for allyl vinyl ether 

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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... 

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. 

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

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. 

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... 

Unfortunately, more heavily substituted hexadienes than those shown in equation (30) do not undergo the rearrangement, presumably because they have very low binding constants with catalytic palladium(II) species. Nevertheless, the Claisen rearrangement of allyl vinyl ethers can only take place provided palladium coordination to the vinyl group is... 

The Claisen rearrangement of allyl vinyl ethers 480 is a fairly general method for the preparation of y, -unsaturated carbonyl compounds of the general formula 481 from simple precursors (Scheme 2.154). ° Synthetically, this transformation is equivalent to the well-known a-allylation of enolates, which gives ultimately the same product. However, the mechanisms and conditions of these two reactions differ and their synthetic potentials are complementary to each other. 

D. L. Severance and W. L. Jorgensen, /. Am. Chem. Soc., 114, 10966 (1992). Effect of Hydration on the Claisen Rearrangement of Allyl Vinyl Ether from Computer Simulations. 

Since its discovery in 1912, the Claisen rearrangement of allyl vinyl ethers (1 - 2 equation 1) has become one of the most powerful tools for stereoselective carbon-carbon bond formation. Much of its current popularity is due to the subsequent development of a series of new variants of this 3,3-sigma-tropic rearrangement. In 1940, Carroll reported the base-catalyzed rearrangement of -keto esters and allylic alcohols to alkenic ketones (3 4 5 equation 2). Twenty years later. Saucy and Marbet dem-... 

The only examples of asymmetric Claisen rearrangements catalyzed by a chiral aluminum catalyst are those published by Yamamoto and coworkers [24-27]. The Claisen rearrangement of allyl vinyl ethers of type 91 (Sch. 13) can proceed via either of the two enantiomeric chair transition states 92 or 94. If a chiral Lewis acid is used to activate the process, the transition states become diastereomeric and preferential formation of one enantiomer of the product is possible. This is complicated because coordination of a chiral Lewis acid to the ether oxygen of allyl vinyl ether produces a new chiral center as indicated in 96 and asymmetric induction might occur from a substituent on aluminum to the oxygen and then from the oxygen to the C-3 carbon in the product. In their initial report, Maruoka, Banno, and Yamamoto found that a catalyst prepared from the 3,3 -disilyl-substituted BINOL 97 and trimethylaluminum was effective in this transformation [24]. The catalyst 98 was shown to be monomeric by measurement of freezing point depression. 

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