Allyl rearrangement, aromatization

Various S-nucleophiles are allylated. Allylic acetates or carbonates react with thiols or trimethylsilyl sulfide (353) to give the allylic sulfide 354[222], Allyl sulfides are prepared by Pd-catalyzed allylic rearrangement of the dithio-carbonate 355 with elimination of COS under mild conditions. The benzyl alkyl sulfide 357 can be prepared from the dithiocarbonate 356 at 65 C[223,224], The allyl aryl sufide 359 is prepared by the reaction of an allylic carbonate with the aromatic thiol 358 by use of dppb under neutral condi-tions[225]. The O-allyl phosphoro- or phosphonothionate 360 undergoes the thiono thiolo allylic rearrangement (from 0-allyl to S -allyl rearrangement) to afford 361 and 362 at 130 C[226],... 

Rearrangements, especially those only involving heat or a small amount of catalyst to activate the reaction, display total atom economy. A classic example of this is the Claisen rearrangement, which involves the rearrangement of aromatic allyl ethers as shown in Scheme 1.2. Although... 

Scheme 10.35 Aromatic Claisen rearrangements of catechol mono allylic ethers with sulfur-containing boron catalyst.

Kitazume and Zulfiqar have investigated the Claisen rearrangement of several aromatic allyl ethers in ionic Hquids, catalyzed by scandium(III) trifluoromethane-sulfonate [72]. The reaction initially gave the 2-aUylphenol but this reacted further to give 2-methyl-2,3-dihydrobenzo[b]furan (Scheme 5.1-41). The yields in this reaction were highly dependant on the ionic liquid chosen, with [EDBU][OTf giving the best yields (e.g., 91 % for R = 6-CH3). Reactions in [BMIMjlBFJ and [BMIM][PF j gave low yields (9-12 %). 

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. 

The B-G bond of allyl-, alkynyl-, aryl-, and benzylboranes is more easily cleaved than that of alkylboranes. The C-B bond of aromatic boronic acids is stable to water, but polyfluorinated phenylboronic acids are exceptionally sensitive to Me0H-H20-K0H and Me0H-H20-pyridine.488 Allylic organoboranes were hydrolyzed with water at room temperature with complete allylic rearrangement (Equation (102)).489,490 Addition of water resulted in the rapid hydrolysis of benzylic G-B bond of 329 due to the electron-withdrawing effect of Cr(CO)3 group (Equation (103)).491... 

The Claisen rearrangement has attracted much attention as an attractive tool for the construction of new carbon-carbon bonds. Taguchi et al. reported the enantioselective and regioselective aromatic Claisen rearrangement of catechol mono allylic ether derivatives by means of Corey s chiral boron reagent (Eq. 70) [53a,54]. The mechanism of enantioselectivity is that a rigid five-membered cyclic intermediate is formed by reaction of catechol mono allylic ethers with the chiral boron reagent and this is fol-... 

Vinyl allyl ethers undergo concerted, 6-center, non-aromatic Claisen rearrangements to unsaturated aldehydes or ketones, viz. 

Wagner-Meerwein and allylic rearrangements are very common whenever a carbonium ion is formed. For example, in the simple Friedel-Crafts alkylation, the alkyl group always tends to rearrange to give the most stable carbonium ion, which then adds to the aromatic ring. In order to prevent this rearrangement,... 

Europium tris(6,6,7,7,8,8,8-heptafluoro-2 -dimethyloctane-3 -dionate). Eu(fod)3 Aromatic Claisen rearrangement Excellent chirality transfer accompanies the rearrangement of allyl aryl ethers. 

Replacement of Hydroxyl When (/(-Codeine is treated with phosphorus pentachloride or thionyl chloride allylic rearrangement occurs and a-chlorocodide is formed [238, 428], /3-Chlorocodide results when -codeine is heated under pressure with concentrated hydrochloric acid, but this doubtless arises by rearrangement of the a-isomer first formed [243], Bromocodide is produced by the interaction of (/(-codeine and phosphorus tribromide [428]. With phosphorus pentachloride dihydro- -codeine-A gives 8-chlorodihydrocodide, with thionyl chloride chlorination only occurs in the aromatic nucleus, and with phosphorus tribromide a poor yield of 8-bromodihydrocodide is obtained [240]. Tetrahydro- r-codeine gives tetrahydro-i/j-cblorocodide with phosphorus pentachloride [295]. 

B. Allyl Aryl Ethers. Aromatic Claisen Rearrangement. 460... 

The overwhelming majority of literature devoted to isomerizations of allyl aryl ethers is connected with the aromatic Claisen rearrangement and is summarized in detail in many reviews . Although the [3,3]-sigmatropic isomerization of phenol ethers to the corresponding C-alkylated derivatives has enjoyed widespread application in organic synthesis for over seventy years, it continues to be a very important reaction for the construction of a carbon-carbon bond. This section presents only recent reports. 

The cyanophosphates resulting from a,p-unsaturated ketones are readily transformed into conjugated allylic phosphate via a BF, FtiO-catalyzed allylic rearrangement (Scheme Similarly, the cyanophosphates derived from 1,4-benzoquinones react with aromatic and heteroaromatic compounds to give 3-aryl-4-hydroxybenzonitriles. ... 

For a consecutive electroeyelic ring closure Claisen rearrangement-intramolecular ami-nation process see refs 206 and 207. For studies on the sequential Claisen rearrangement of methyl-3-aryloxy-2-(aryloxymethyl)prop-2-enoates see ref 208 and for the base-catalyzed aromatic Claisen rearrangement of 3-hydroxyphenyl allyl ethers, cf. ref 209. 

Rearrangement of selenilimines obtained by the oxidation of allylic selenides affords a route to allylic secondary amines.[31] Amines obtained by allylic rearrangement were prepared by treating a variety of aliphatic or aromatic primary amines with an allylic selenide activated by N-chlorosuccinimide (Scheme 28). 

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