Crotonates cleavage

The reaction with hydroxide ion is frequently used as proof for the chemical structure of cyclopropenones and has been examined in some detail with respect to the factors governing ring-cleavage. Thus, methyl cyclopropenone23 and aqueous NaOH react to yield a mixture of methacrylic and crotonic acids in a ratio of 3 1 as expected from the relative stabilities of the two possible intermediate carbanions (type 317) ... 

Diastereoselective aldol reactions The boryl enolates of chiral crotonate imides (1) and (2) react with aldehydes to form adducts (3) and (4), respectively, with high diastereoselectivity and complete a-regioselectivity. The method of choice for reductive cleavage of the adducts is formulated for 3 hydrolysis can also be effected with LiOH and H202. 

Based on our previous results on the nucleophilic alkenoylation of aldehydes via metallated a, 3-unsaturated aminonitriles [50], we now envisaged an enanti-oselective variant. Thus, the enantiopure a-aminonitriles 60 were metallated with LDA and by reaction with aldehydes the adducts 61 could be obtained. Subsequent cleavage of the aminonitrile function with silver nitrate led to the desired a -hydroxyenones 62 in overall yields of 29-80% and enantiomeric excesses ee of 50-69%. Alternatively, the conjugate addition of the lithiated aminonitrile 63 to t-butyl crotonate led to the y-keto ester 63 in 35% yield and an enantiomeric excess ee of >90% (Scheme 1.1.18). 

A DIE of k 2o/k )2o = 3.2 has been found in the hydrolysis of a-benzoyloxystyrenes, 382, in concentrated perchloric acid solution450. The rate of hydrolysis was found to be linear with the acidity function, Ho- A small inverse deuterium KIE, A h /I d = 0.78, at the -carbon has been found in the oxidation of cinnamic and crotonic acids451 by quinolinium dichromate. The reaction involves electrophilic attack on the double bond and a carbonium-ion intermediate (p = —4.0). A small inverse D KIE (k /k ->) = 0.80, p = —4.0] has been also observed452 in the acid cleavage of substituted styrenes by quinolinium dichromate in DMF in the presence of acid452. 

The C-0 bond in vinyl esters can also be cleaved promoted by Ru(0) complex to give vinylruthenium complex (Eq. 23) [64]. Another example of the vinyl-O bond cleavage has been recently reported in the treatment of vinyl crotonate with a (perfluorophenyl)palladium complex. The reaction course has been accounted for by insertion- 3-elimination processes (Eq. 24) [57]. 

A pure hydrolytic decomposition of hydrophobic PHB is, in contrast to the enzymatic decomposition under the same experimental conditions, about 2-3 times slower, but increases with growing pH-value and temperature. Under high-temperature conditions, above the melting point, the PHB is subjected to the formation of linear oligomers as a result of ester cleavage and/or a jS-elimination, and this resulted in crotonic acid. 

Some of the early uses [13] of MCPBA indicate the initial objectives that one would consider when evaluating new potential substitutes. The epoxidation of alkenes such as 1-octene (Eq. 1) and ethyl crotonate (Eq. 2), and the epoxidation of enol ethers followed by cleavage (Eq. 3) [14] are illustrative. 

Esterification, crotonic acid, 149 levulinic acid, 157 thiophene-2-carboxylic acid, 182 o-toluic acid, 162 Ester interchange, 152 Ethanolysis of ethyl iminoacetate, 159 Ether cleavage with HBr, 271... 

CH3OH) across the carbon-carbon double bond of crotonic acid [( )-2-butenoic acid] followed by potassium bromide treatment of the initial adduct to yield the corresponding mercuric bromide and then the formation of 2-bromo-3-methoxybutanoic acid by the addition of bromine (Br2) to the latter. Acidification to the free acid, followed by amination (NH3), formylation with the equivalent of acetic-formic anhydride, hydrogen bromide (HBr) ether cleavage, and a final pH adjustment with ammonium hydroxide produced the desired amino acid. 

Cannabimovone (CBM, 8), isolated from a non-psychotropic variety of C. saliva (Carma) [16], is characterized by an unprecedented abeo-menthane terpenoid stmcture, which can be rationalized in terms of dihydroxylation of the endocyclic double bond of CBD, followed by oxidative cleavage of the glycol system and then aldolization of the resulting dicarbonyl. Attempts to mimic this pathway led only to the crotonized analog of the natural product. 

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