Ketones, acid catalyzed rearrangement

A carbonyl transposition can be effected via the addition of a vinyl or an alkyl Grignard reagent to an a, 3-unsaturated ketone. Acid-catalyzed rearrangement of the resultant allylic alcohol during oxidation with PCC affords the transposed a,(3-unsaturated carbonyl substrate. This reaction represents a useful alternative when Wittig olefination of the ketone is problematic. 

Garyophyllene. (-)-CaryophyUene can be isolated from Indian turpentine and has been used to prepare a number of woody aroma products. The epoxides are produced by reaction with peracids. Acetylation of caryophyUene also gives a usehil methyl ketone (180) (Fig. 8). Acid-catalyzed rearrangement of caryophyUene in the presence of acetic acid gives a mixture of esters, which are related to caryolan-l-ol and clovan-2-ol (181). 

The preparation of neopentyl alcohol from diisobutylene herein described represents an example of acid-catalyzed addition of hydrogen peroxide to a branched olefin, followed by an acid-catalyzed rearrangement of the tertiary hydroperoxide formed. In addition to neopentyl alcohol, there are formed acetone and also small amounts of methanol and methyl neopentyl ketone by an alternative rearrangement of the hydroperoxide. 

Sulfur ylides can also transfer substituted methylene units, such as isopropylidene (Entries 10 and 11) or cyclopropylidene (Entries 12 and 13). The oxaspiropentanes formed by reaction of aldehydes and ketones with diphenylsulfonium cyclopropylide are useful intermediates in a number of transformations such as acid-catalyzed rearrangement to cyclobutanones.285... 

The ketone (265) was able to rearrange to isophyllocladenone (267) when heated in benzene in the presence of excess pTsOH, presumably via the acid catalyzed rearrangement of the intermediate (266)9i). 

Treatment of the ketone (287) with pTsOH in benzene at 60 °C provided the norbornen-7-one derivative (288)98), following interesting acid-catalyzed rearrangement. 

Acid-catalyzed rearrangement of tertiary a-acetylenic (terminal) alcohols, leading to the formation of a,(3-unsaturated ketones rather than the corresponding a,(3-unsaturated aldehydes. Cf. Meyer-Schuster rearrangement. 

By-products of the direct excitation of 104 were the isomeric cis- and main products of the triplet-sensitized excitation of 104 in the presence of ketones. Acid-catalyzed prototropic rearrangement of a colorless precursor (141) was suggested to account for formation of 142. ... 

Butene is oxidized to methyl ethyl ketone, presumably arizing from the acid-catalyzed rearrangement of the peroxide. Alkenols and aldehydes are formed in lower amounts. Cyclopentene is more reactive towards oxidation than butenes. 

Interestingly, Lewis acid catalyzed rearrangement of 6-methyltricyclo[8.2.0.0, 6]dodecan-9-one gave the spiroannulated triquinane ketone (l/ , 5/ )-l-methylspiro[bicyclo[3.3.0]octane-2,lf-cyclopentane]-6-one as the major product (70%).85... 

Acid-Catalyzed Rearrangements of Aldehydes and Ketones 1 /Alkyl,2/alkyl-interchange, etc. 

Synthetic methods for 2(5jF/)-furanones have been developed in the preparation of cardenolides (65MI31200). The ketone (171) when reacted with lithium ethoxyacetylide gives the carbinol (172) which undergoes acid catalyzed rearrangement to the a,/3-unsaturated ester (173). Allylic oxidation of (173) with selenium dioxide under mild conditions gives digitoxigenin acetate (174) (Scheme 38). 

The acid-catalyzed rearrangement of 377 and 379 afforded 378 and 380, respectively, in good yields. The tricyclic ketone 380 contains all appropriate functionality for the synthesis of the atisine-type alkaloids, ajaconine and atidine. 

In fluorinated alcohol solvents, nonstrained ketones such as cyclohexanone (1) undergo oxidation to lactones in the presence of hydrogen peroxide and catalytic amounts of Brpnsted acids (Berkessel and An-dreae 2001 Berkessel et al. 2002). Unlike the classical Baeyer-Villiger reaction, ketone oxidation with H2O2 in e.g. HFIP proceeds via a spiro-bisperoxide 2 intermediate (Scheme 1). In contrast to other solvents, the acid-catalyzed rearrangement of the spiro-bisperoxide 2 to two equivalents of the product lactone 3 proceeds rapidly and cleanly in HFIP. Preliminary calculations indicate active participation of the fluorinated alcohol solvent in the rate-determining step also in this case. 

Cargill RE, Jackson TE, Peet NP, Pond DM (1974) Acid-catalyzed Rearrangements of P,Y-Unsaturated Ketones. Acc Chem Res 7 106... 

The acid catalyzed rearrangement of tertiary acetylenic alcohols, the Rupe reaction, is a viable procedure for the preparation of a,p-unsaturated carbonyl compounds. Under standard acidic conditions, however, the products can polymerize and various by-products can be produced. With solid acids these problems are minimized. The reaction of an acetylenic tertiary alcohol with Nafion-H gave the a,P-unsaturated ketone in good to very good yields (Eqns. 22.24—25). When this reaction was run using a vanadium pillared... 

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