Alkene To acid

Table 3.6 Oxidative cleavage of alkenes to acids and alkynes to ketones or acids...

S-8-S carbon skeleton of Aisicoccins and ophiobolins (equation 10). Trisubstituted alkenes yield keto acids (equation 11). A related reaction, known as the Lemieux-von Rudloff (periodate-permanganate) oxidation, is also used to oxidize alkenes to acids or ketones (equation 12). If aldehydes are required... 

A second strategy using pyruvate as a source for the C-1 and C-2 carbons of the nascent citramalate is based on an ene reaction with a-ketoesters. Reaction between the pyruvate ester of (— )- ra 5 -2-phenylcyclohexanol (1061) and allyltrimethylsilane in the presence of tin tetrachloride produces adduct 1062 as a single diastereomer. Oxidation of the alkene to acid 1063 followed by base hydrolysis and esterification gives dimethyl (R)-citramalate (1059) with 96% optical purity (Scheme 158) [228]. 

Ketones are far less susceptible to oxidation than aldehydes and are readily prepared by oxidation of appropriately substituted alkenes and secondary alcohols. The conditions given in Sections 6.1.1 and 6.2.1 for oxidation of alkenes to acids or aldehydes are applicable for ketones as well. 

Alkylation combines lower-molecular-weight saturated and unsaturated hydrocarbons (alkanes and alkenes) to produce high-octane gasoline and other hydrocarbon products. Conventional paraffin-olefin (alkane-alkene) alkylation is an acid-catalyzed reaction, such as combining isobutylene and isobutane to isooctane. 

Higher terminal alkenes are oxidized to methyl ketones and this unique oxidation of alkenes has extensive synthetic applications[23]. The terminal alkenes can be regarded as masked methyl ketones, which are stable to acids, bases, and nucleopliiles[24]. The oxidation of terminal alkenes to methyl ketones has been extensively applied to syntheses of many natural products[77]. 

A interesting and useful reaetion is the intramolecular polycyclization reaction of polyalkenes by tandem or domino insertions of alkenes to give polycyclic compounds[l 38]. In the tandem cyclization. an intermediate in many cases is a neopentylpalladium formed by the insertion of 1,1-disubstituted alkenes, which has no possibility of /3-elimination. The key step in the total synthesis of scopadulcic acid is the Pd-catalyzed construction of the tricyclic system 202 containing the bicyclo[3.2. Ijoctane substructure. The single tricyclic product 202 was obtained in 82% yield from 201 [20,164). The benzyl chloride 203 undergoes oxidative addition and alkene insertion. Formation of the spiro compound 204 by the intramolecular double insertion of alkenes is an exam-ple[165]. 

We can gam a general understanding of the mechanism of hydrogen halide addi tion to alkenes by extending some of the principles of reaction mechanisms introduced earlier In Section 5 12 we pointed out that carbocations are the conjugate acids of alkenes Therefore strong acids such as HCI HBr and HI can protonate the double bond of an alkene to form a carbocation... 

Acids other than hydrogen halides also add to the carbon-carbon bond of alkenes Concen trated sutfuric acid for example reacts with certain alkenes to form alkyl hydrogen sulfates... 

Acid catalyzed hydration converts alkenes to alcohols with regioselectivity according to Markovnikov s rule Frequently however one needs an alcohol having a structure that corresponds to hydration of an alkene with a regioselectivity opposite to that of Markovnikov s rule The conversion of 1 decene to 1 decanol is an example of such a transformation... 

Oxidation of tridecylborane gives 1 decanol The net result is the conversion of an alkene to an alcohol with a regioselectivity opposite to that of acid catalyzed hydration... 

Peroxy acid and alkene Transition state for oxygen transfer from the OH group of the peroxy acid to the alkene Acetic acid and epoxide ... 

Epoxidation (Section 6 18) Peroxy acids transfer oxygen to the double bond of alkenes to yield epoxides The reaction IS a stereospecific syn addition... 

Addition of phenylmagnesium bromide to 4 tert butylcyclohexanone gives two isomeric ter tiary alcohols as products Both alcohols yield the same alkene when subjected to acid catalyzed dehydration Suggest reasonable structures for these two alcohols... 

Epoxidation (Section 6 18) Conversion of an alkene to an epoxide by treatment with a peroxy acid... 

A catalyst, usually acid, is required to promote chemoselective and regioselective reduction under mild conditions. A variety of organosilanes can be used, but triethylsilane ia the presence of trifiuoroacetic acid is the most frequendy reported. Use of this reagent enables reduction of alkenes to alkanes. Branched alkenes are reduced more readily than unbranched ones. Selective hydrogenation of branched dienes is also possible. 

Since a carbocation can add to an alkene to form a larger cation, under acidic conditions isobutylene can dimerize to form 2,4,4-trim ethyl -1 -pen ten e [107-39-1] and 2,4,4-trimethyl-2-pentene [107-40-4J, which can then be hydrogenated in the presence of nickel to form isooctane [540-84-1]. This reaction is no longer of commercial significance. 

Diazo compounds react with alkenes to afford A -pyrazolines, which in turn izomerize to A -pyrazolines if there is a hydrogen atom a to the N=N bond (Scheme 54). In those cases where two possible ways of isomerization exist, the more acidic hydrogen migrates preferentially. The alkene configuration is conserved on the A -pyrazoline (stereospecificity) but the regioselectivity depends on the substituents of both the alkene and the diazo compound. 

Rahman and Clapp decomposed dinitromethane derivatives in DMF in the presence of alkenes to obtain 2-isoxazolines. Without any alkene present, an acid and KNO2 were obtained. They proposed a mechanism which proceeded via a three-membered ring or a nitrocarbene which rearranged to a nitrile oxide (76JOC122, 75MI41612). 

Nitrones or aci-nitro esters react with alkenes to give in some cases A/-substituted isoxazolidines and in others 2-isoxazolines. When the intermediate isoxazolidines were observed, a number of procedures transformed them into the 2-isoxazolines. Acrylonitrile and phenyl rzcf-nitrone esters produced an A/-methoxyisoxazolidine. Treatment with acid generated a 2-isoxazole while treatment with base generated an oxazine (Scheme 118) (68ZOR236). When an ethoxycarbonyl nitrone ester was reacted with alkenes, no intermediate isoxazolidine was observed, only A -isoxazolines. Other aci-mtro methyl esters used are shown in Scheme 118 and these generate IV-methoxyisoxazolidines or A -isoxazolines which can be further transformed (72MI41605). 

Strong acids also catalyze the addition of alcohols to alkenes to give ethers, and the mechanistic studies which have been done indicate that the reaction closely parallels the hydration process. ... 

The electrophile in oxymercuration reactions, HgX or Hg " , is a soft acid and strongly polarizing. It polarizes the n electrons of an alkene to the extent that a three-center, two-... 

Peroxy acid oxidation of alkenes (Sections 6.18 and 16.9) Peroxy acids transfer oxygen to alkenes to yield epoxides. Stereospecific syn addition is observed. 

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