Claisen-rearrangement

The Claisen rearrangement has attracted much attention as an attractive tool for the construction of new carbon-carbon bonds. Various catalytic systems have been developed to afford enantioselective versions of this process. On the other hand, relatively few chiral sulfur-containing ligands have been investigated for this type of reaction. As an example, Taguchi et al. have 

Further rearrangement of the normal ort/zo-Claisen rearrangement produet gives the /7flra-Claisen rearrangement produet. 

SCHEME 9A Synthesis of 2-C-methylene-a-D-glucosides and aromatic pyranopyrans via the Perrier rearrangement. 

Other important, practical approaches to C-glycosides and S-thioglycosyl derivatives were reported by Descotes et al. [13] and Osborn et al. [14]. 

The Claisen rearrangement [15] is one of the most useful approaches to many C-linked functionalized carbohydrate derivatives. Werschkun and Thiem [16] reviewed the applications of the Claisen rearrangement in carbohydrate chemistry, its synthetic accessibility as well as generality of the approach and its synthetic utilization. 

The Claisen rearrangement offers a very useful approach to synthesizing rare sugars functionalized at strategically important positions, which could be used as intermediate templates to more complex natural products [15]. 

Other important example of the Claisen rearrangement reaction is the synthesis of a functionalized template during a long asymmetric synthetic route to natural product, tetrodotoxin, accomplished by Isobe [18]. The rearrangement reaction is the 

For preparation of allyl coumarins and dihydrofuranocoumarins by tandem Claisen rearrangement-cyclization the usual procedures required vigorous reaction conditions, workup procedures were tedious, and long reaction times led to low yields. The rearrangement of allyloxycoumarins 48 to dihydrofuranocoumarins 49 has been optimized in good yields in a sealed Teflon containers with BF3-ether in N-methyl- 

The thermal rearrangement of allyl phenyl ethers to o-allyl phenol and its mechanism is very well known to organic chemists. Both the aliphatic and aromatic Claisen rearrangements involve a 3,3-sigmatropic shift. There are reviews providing usefulness of this rearrangement reaction.  

The corresponding ester also underwent similar rearrangement. Similarly both allyl vinyl ether and 2-hepta-3,5-dienyl vinyl-ether underwent 3,3-shift. The best results were obtained in 2/1 methanol-water the rates were about 40 times than those in acetone solvent.  

The above rearrangement for protected analog under usual claisen condition resulted in elimination of acetaldehyde.  

Following are given some of the important applications of Claisen rearrangement in aqueous solution. 

Metal-catalyzed isomerization of unsymmetrical diallyl ethers is a unique route to synthesize allyl vinyl ethers for the Claisen rearrangement. In 1977, Reuter and Salomon reported that heating the diallyl ether 23 in the presence of a catalytic amount of tris(triphenylphosphine)ruthenium(II) dichloride resulted in the 

which then underwent Claisen rearrangement to produce the y,8-unsaturated aldehyde 30 (syn/anti =95 5) without loss of optical purity. 

Taguchi and coworkers have reported that the chiral C2-symmetric bromoboron Lewis acid (64) promotes the enantioselective Claisen rearrangement of difluo-rovinyl allyl ethers (63) to give hydroxy ketone products (65) in moderate to good enantioselectivity (Equation 40) [40]. 

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Claisen Rearrangements - allyl vinyl ether to an y,5-unsaturated carbonyl... 

Chorismate Mutase catalyzed Claisen Rearrangement- 10 rate enhancement over non-enzymatic reaction... 

Claisen rearrangement usually proceed by a chair-like T.S. 

You have already seen that a carbon-heteroatom bond is easy to make, since we used such bonds as natural places for disconnections (frames 234 ft). It is good strategy therefore to make a carbon-heteroatom bond and then to transform it into a carbon-earbon bond. The Claisen rearrangement is one way to do this an ortho allyl phenol (B) made from an allyl ether (A) ... 

In an imioortant industrial process, the Carroll reaction , an ahphatic version of the Claisen rearrangement occurs. See if you can find the right mechanism ... 

A highly successful route to stereoisomers of substituted 3-cyclohexene-l-carboxylates runs via Ireland-Claisen rearrangements of silyl enolates of oj-vinyl lactones. The rearrangement proceeds stereospeaifically through the only possible boat-like transition state, in which the connecting carbon atoms come close enough (S. Danishefsky, 1980 see also section 4.8.3, M. Nakatsuka, 1990). 

Conjugate addition of vinyllithium or a vinyl Grignard reagent to enones and subsequent oxidation afford the 1.4-diketone 16[25]. 4-Oxopentanals are synthesized from allylic alcohols by [3,3]sigmatropic rearrangement of their vinyl ethers and subsequent oxidation of the terminal double bond. Dihydrojasmone (18) was synthesized from allyl 2-octenyl ether (17) based on Claisen rearrangement and oxidation[25] (page 26). 

Allylic Rearrangement, Claisen Rearrangement, and Related Reactions Catalyzed by Pd(0) and Pd(II)... 

Conversion of 5-allylthioimidates into /V-allylthioamides is catalyzed by Pd(Il). 2-Allylthiopyridine (820) is converted into the less stable l-allyl-2-thio-pyridone 821 owing to Pd complex formation[509], Claisen rearrangement of 2-(allylthio)pyrimidin-4-(3//)-one (822) affords the A-l-allylation product 823 as the main product rather than the A -3-allylation product 824[510] The smooth rearrangement of the allylic thionobenzoate 825 to the allyl thiolo-benzoate 826 is catalyzed by both PdCl2(PhCN)2 and Pd(Ph3P)4 by different mechanisms[511],... 

Q The mechanism of the Claisen rearrangement of other allylic ethers of phenol is analogous to that of allyl phenyl ether What is the product of the Claisen rearrangement of C6H50CH2CH CHCH3 /... 

The transition state for the first step of the Claisen rearrangement bears much m common with the transition state for the Diels-Alder cycloaddition Both involve a con certed six electron reorganization... 

Section 24 13 On being heated allyl aryl ethers undergo a Claisen rearrangement to form o allylphenols A cyclohexadienone formed by a concerted six tt electron reorganization is an intermediate... 

Claisen rearrangement (Section 24 13) Thermal conversion of an allyl phenyl ether to an o allyl phenol The rearrange ment proceeds via a cyclohexadienone intermediate... 

Sigmatropic rearrangement (Section 24 13) Migration of a a bond from one end of a conjugated tt electron system to the other The Claisen rearrangement is an example... 

The most recent, and probably most elegant, process for the asymmetric synthesis of (+)-estrone appHes a tandem Claisen rearrangement and intramolecular ene-reaction (Eig. 23). StereochemicaHy pure (185) is synthesized from (2R)-l,2-0-isopropyhdene-3-butanone in an overall yield of 86% in four chemical steps. Heating a toluene solution of (185), enol ether (187), and 2,6-dimethylphenol to 180°C in a sealed tube for 60 h produces (190) in 76% yield after purification. Ozonolysis of (190) followed by base-catalyzed epimerization of the C8a-hydrogen to a C8P-hydrogen (again similar to conversion of (175) to (176)) produces (184) in 46% yield from (190). Aldehyde (184) was converted to 9,11-dehydroestrone methyl ether (177) as discussed above. The overall yield of 9,11-dehydroestrone methyl ether (177) was 17% in five steps from 6-methoxy-l-tetralone (186) and (185) (201). 

R)-Pantolactone is also prepared in a sequence involving Claisen rearrangement of the chiral glycolate (24), although with poor enantioselectivity... 

AHyl phenyl ethers rearrange cleanly at high temperatures, producing o-aHyl phenols or -aHylphenols if both ortho positions are blocked. This reaction is called the Claisen rearrangement (10). 

A heterocyclic ring induces partial double-bond fixation in a fused benzene ring. Hence, for example, diazo coupling occurs at the 7-position of 6-hydroxyindazole (349), and Claisen rearrangement of 6-allyloxy-2-methylbenzothiazole (350) gives the 7- and 5-allyl products in a ratio of 20 1. 

From the results quoted in Section 4.04.2.1.3(x) the stability of acetyl derivatives of indazolone decreases in the order Af(l)-acetyl >A (2)-acetyl > 0(3)-acetyl. The reactivity of 3-hydroxypyrazoles is covered by Dorn s comprehensive review (80CHE1). Amongst the results reported there are the Claisen rearrangement of allyloxypyrazoles (475a) (475b)... 

Alkylation of 3-methyl-4-phenylisoxazolin-5-one with allyl bromide gave a mixture of N- and C(4)- alkylation in a 2 1 ratio. Heating the mixture changed the ratio to 1 99 and this conversion is believed to take place by an amino-Claisen rearrangement (Scheme 91) (69TL543). 

H-Azepine, 2-allyloxytetrahydro-Claisen rearrangement, 7, 508 3H-Azepine, 2-amino-acylation, 7, 511 effect of acidification, 7, 510 nucleophilic displacement reactions, 7, 514 synthesis, 7, 533, 535 3H-Azepine, 2-amino-7-bromo-synthesis, 7, 529 3H-Azepine, 2-anilino-ring inversion, 7, 495-499 structure, 7, 533... 

H -Azepin-2-one, 4-allyloxytetrahydro-Claisen rearrangement, 7, 508 1 H-Azepin-2-one, hexahydro-conformation analysis, 7, 499 mass spectra, 7, 501... 

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