Claisen rearrangement, aliphatic

Secondary aliphatic amines were found to give higher yields of thienothiophenes than did tertiary amines, which are weaker bases. A maximum ratio of thienothiophenes to thienothiopyrans of about 4 1 was achieved at 145° with diisopropylamine as cat yst and DMSO as solvent. Only thienothiopyrans were formed in DMF in the presence of the same catalyst The amines promote nucleophilic cyclization of Claisen rearrangement products into thienothiophenes. Since thienothiophenes are resistant to treatment with potassium t-butoxide in DMSO and thienothiopyrans form resinous products under these conditions, the method is a convenient route to pure thienothiophenes 35 and 42 in yields of up to 40%. ... 

The ruthenium-catalyzed direct addition of saturated aliphatic alcohols to non-activated alkynes remains a challenge. Only ally alcohol has been successfully involved in the intermolecular addition to phenylacetylene to produce an ether and the enal resulting from Claisen rearrangement (Equation 10.7) [24]. Thus, in refluxing toluene, in the presence of a catalytic amount of RuCl(tris(pyrazolyl) borate) (pyridine)2, a 1 1 mixture of ally P-styryl ether and 2-phenylpent-4-enal was obtained in 72% overall yield. 

In this section, the aliphatic Cope and Claisen rearrangements, as depicted in the transformation of I to 2 in Scheme 2, are discussed, as well as variations of the latter (i.e.. Johnson-Claisen, Ireland-Claisen, Reformatsky Claisen, F.schenmoser-Claisen. Ficini Claisen, and hetero-Claisen rearrangements). When X is oxygen, replacement of Cl and C2 with an aromatic ring... 

Aliphatic Claisen Rearrangements Fluorine Substitution on the Vinyl Fragment... 

This method offers an alternative to the reaction of allylic alcohols with tetrafluoroethene to form acids 3 via an aliphatic Claisen rearrangement (see Section 5.1.5.2.). The reaction of la is four times as fast as that of allyl trjchloroacetate under similar conditions. In the absence of chlorotrimethylsilane, no rearrangement occurs. 

Aliphatic Claisen rearrangement,4 Allyl vinyl ethers undergo [3, 3] sigmatropic rearrangement in the presence of (CH3)3A1 or (C2H5)3A1 with substitution of CH3 or C2H5 on the aldehydic carbon atom (equation I). 

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

We used the all-carbon Cope rearrangement 29 to introduce this section but now we want to feature the more useful Claisen rearrangements.14 The aliphatic Claisen 54 works for most substituents because an alkene is lost and a much more stable carbonyl group is formed 55. It doesn t matter whether we have an aldehyde (X = H), a ketone, (X = R), an acid (X — OH), an ester (X = OR) or an amide (X = NR2), the reaction works well. The original Claisen rearrangement was the aromatic version 56 that gives an unstable non-aromatic intermediate 57 that quickly loses a proton to restore the aromatic ring and the product is a phenol 58. 

The aliphatic Claisen rearrangement is simpler in that there is no rearomatisation at the end but there is an ionic step first as the vinyl ether 67 has to be made and the easiest way to do that is from the allylic alcohol 65 by acetal exchange with another vinyl ether to give 66 and elimination to give 67. All these steps, including the rearrangement occur under the same conditions16 and the product is a y,S-unsaturated carbonyl compound 68. 

In the last chapter we used 79 in an aliphatic Claisen rearrangement to make an anisatin intermediate. You can now see that 79 was made by Birch reduction of 80. With a Friedel-Crafts in mind, we change the alcohol for a ketone 81 and start with 82. 

The presence of jr-electron-donating substituents at the 2-position of the vinyl portion of the ether allows for significant acceleration of the Claisen rearrangement.314-318 Aliphatic Claisen rearrangements can proceed in the presence of organoaluminum compounds,286-319-320 although other Lewis acids have failed to show reactivity.286,321 324 Useful levels of (Z)-stereoselection and asymmetric induction have been obtained by use of bulky chiral organoaluminum Lewis acids.325 327... 

The experimental KIEs were determined for the aliphatic Claisen rearrangement in p-cymene at 120°C and for the aromatic Claisen rearrangement either neat at 170°C or in diphenyl ether at 220°C. Changes in 2H, 13C or 170 composition were determined for unreacted substrates. For carbon analysis of allyl vinyl ether the C5 carbon was used as an internal standard. The C4 atom and rneta aryl protons were used as references in analysis of allyl phenyl ether. The 170 analysis was based on a new methodology. The results are summarized in Table 1, along with predicted isotope effects calculated for experimental temperatures by means of different computational methods. The absolute values of predicted isotope effects for C4 and C5 atoms varied with theoretical level and all isotope effects were rescaled to get reference effects equal to 1.000. 

Jn an important industrial process, the "Carroll reaction", an aliphatic version of the Claisen rearrangement occurs. See if you can find the right mechanism ... 

F. E. Ziegler, The thermal aliphatic Claisen rearrangement, Chem. Rev. 1988,88, 1423. 

It was later found that the same sort of reaction occurs without the aromatic ring. This is called either the aliphatic Claisen rearrangement or the Claisen-Cope rearrangement. Here is the simplest possible example. 

The starting material for these aliphatic Claisen rearrangements consists of ethers with one allyl and one vinyl group. We need now to consider how such useful molecules might be made. There is no problem about the allyl half—allylic alcohols are stable easily made compounds. But what about the vinyl half Vinyl alcohols are just the enols of aldehydes (MeCHO). The solution is to use an acetal of the aldehyde in an acid-catalysed exchange process with the allylic alcohol. 

Table 5 Rate Constants for the Aliphatic Claisen Rearrangement of Sodium Caiboxylate (222) and Methyl Ester...

The ability of charged substituents to accelerate the 3,3-sigmatropic reiarrangement of allyl vinyl ethers (the Claisen rearrangement) has also been documented. The effect of oxyanion substituents on the rate and course of aliphatic Claisen rearrangements has been the subject of particular attention. " In 1972, Ireland and Mueller reported that the lithium enolate derivatives of allyl esters undergo rapid and effi-... 

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