Vinyl ethers rearrangement

Cyclopropane 87, obtained from n-butyl vinyl ether, rearranges to dihydrofuran 88 only at elevated temperature, and also partly during work-up on silica gel113). The complete conversion of 87 into veratrole by the action of HCl/CH3OH gave rise to the analogous two-step synthesis of hydrourushiol monomethyl ether from l-diazo-3,3-dimethoxy-2-nonadecanone 89113). Ether cleavage of the product yields hydrourushiol, one of the vesicant components of, inter alia, poison ivy. 

In addition to the classical allyl vinyl ether rearrangement, several variations have been developed which improve the synthetic value of the Claisen rearrangement with respect to the preparation of the parent compounds, reaction conditions and stereoselectivity. 

The different stereochemical course has been explained by unfavorable steric interactions of the methoxy group and the ring proton in the chair transition state B for the ortho ester variant resulting in a preference for the boatlike transition states C and D. On the other hand, chair transition state A predominates in the allyl vinyl ether rearrangement of 7 and 8. 

D.i. Allyl-Vinyl Ether Rearrangements. This reaction predated the Cope rearrangement and is obviously very similar. An alkenyl carbonyl product is obtained just as in the oxy-Cope rearrangement, but the carbonyl is generated directly rather than via initial enol formation. As with the Cope rearrangement, the... 

The Claisen-Johnson rearrangement is also a reaction of choice for the construction of quaternary centers in the synthesis of triquinanes and related ter-penes. Accordingly, transposition of aUyUc alcohol 125 is a cornerstone reaction in the synthesis of tricyclic compound 124, a key intermediate for the access to several triquinanes described by Iwata [28] (Scheme 6.17). Acid 126 was obtained in 57% yield after transposition and saponification. Claisen allyl vinyl ether rearrangement was also applied to allylic alcohol 125. Oxidation of the aldehyde inter-... 

Tsuji [69], in a stereoselective synthesis of de-AB-cholestan-9-one 315, studied an orthoester rearrangement followed by an allyl vinyl ether rearrangement affording the advanced intermediate 319 (Scheme 6.50). 

For related studies using the allyl vinyl ether rearrangement, see G. Rackur,... 

This chapter will discuss 1,3-dienes in a reaction with alkenes to give cyclohexene derivatives. This is a thermal reaction driven by interactions of molecular orbitals rather than ionic or polarized intermediates. In addition to the reaction of 1,3-dienes, 1,5-dienes undergo a rearrangement to a different 1,5-diene in what is known as a sigmatropic rearrangement. Similarly, allyl vinyl ethers rearrange to form alkenyl aldehydes or ketones. Both of these reactions tend to give difunctional molecules as products. 

The importance of the base used in the [2,3]-Wittig reaction is made clear by the work of Mitchell and coworkers who have reported the rearrangements of silyl- and stannyl-substituted diallyl ethers. They found that the use of LDA on such substrates (38, 41, 43) leads to [2,3]-Wittig reaction while employing lithium diethylamide can result in an allyl-vinyl ether rearrangement instead. 

The Claisen rearrangement is another important pericyclic reaction that is dramatically accelerated by aqueous solvents. The effect of solvation on this reaction has been studied extensively both experimentally and theoretically. For the allyl vinyl ether rearrangement (Scheme 6), Monte Carlo simulations have shown that both the number and the strength of solvent hydrogen bondings to the oxygen atom contribute to the rate acceleration of the reaction. Using the continuum AM1-SM2 solvation model, Cramer and Truhlar concluded... 

One of the metabolic reactions in the biosynthesis of the amino acid phenylalanine occurs by a [3,3] sigmatropic shift in a reaction called a Claisen rearrangement. In this reaction, chorismate, a vinyl ether, rearranges to prephenate. 

A Schmittel cyclization has been reported using a triazole-gold-eatalysed propargyl vinyl ether rearrangement (Seheme 120). ... 

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