Alkene cleavage acids

Alkene Cleavage to Aldehydes, Ketones or Acids (3.2 Tables 3.3, 3.6)... 

Abstract This chapter covers one of the most important areas of Ru-catalysed oxidative chemistry. First, alkene oxidations are covered in which the double bond is not cleaved (3.1) epoxidation, cis-dihydroxylation, ketohydroxylation and miscellaneous non-cleavage reactions follow. The second section (3.2) concerns reactions in which C=C bond cleavage does occur (oxidation of alkenes to aldehydes, ketones or carboxylic acids), followed by a short survey of other alkene cleavage oxidations. Section 3.3 covers arene oxidations, and finally, in section 3.4, the corresponding topics for aUcyne oxidations are considered, most being cleavage reactions. 

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

Natural ProductfPharmaceutical Syntheses Involving Alkene Cleavage to Acids... 

An aldol reaction in acid solution ensures that the more substituted enol is formed and the aldehyde is by far the most electrophilic of all the carbonyl groups. The Diels-Alder reaction gives the free acid 30 which was resolved with a chiral amine and each enantiomer used for a different part of the B12 molecule. The slightly unusual reagent Cr(VI) was used for the alkene cleavage and acetal formation occurred spontaneously under the acidic conditions. 

Diols are oxidatively cleaved by reaction with periodic acid (HIO4) to yield carbonyl compounds, a reaction similar to the KMnO cleavage of aJkenes just discussed. The sequence of (1) alkene hydroxylation with OsO< j followed by (2) diol cleavage with HIO4 is often an excellent alternative to direct alkene cleavage with ozone or potassium permanganate. 

Another alkene cleavage method is illustrated by the conversion of the alcohol moiety in 5.228 (the template) to a mesylate and then to azide 5.229. Oxidative cleavage with periodate and ruthenium trichloride was followed by hydrogenation of the azide to give 3-amino-2-methylpentanoic acid, 5.230. 

Can you remember what re action of an alkene would give the same products as the periodic acid cleavage shown here" ... 

The chemical inertness of the three-membered ring permitted many conversions of functional groups in diazirines. Esterifications, cleavage of esters and acetals, synthesis of acid chlorides, oxidation of hydroxy groups to carboxyl groups as well as Hofmann alkenation all left the three-membered ring intact (79AHC(24)63). 

Show the structures of alkenes that give the following products on oxidative cleavage with KMn04 in acidic solution ... 

Alkynes, like alkenes, can be cleaved by reaction with powerful oxidizing agents such as ozone or KMnC, although the reaction is of little value and we mention it only for completeness. A triple bond is generally less reactive than a double bond and yields of cleavage products are sometimes low. The products obtained from cleavage of an internal alkyne are carboxylic acids from a terminal alkyne, CO2 is formed as one product. 

Oxidative cleavage of an alkene with Klvln04 gives a carboxylic acid if the alkene has at least one vinylic hydrogen (Section 7.9). 

Methods of synthesis for carboxylic acids include (1) oxidation of alkyl-benzenes, (2) oxidative cleavage of alkenes, (3) oxidation of primary alcohols or aldehydes, (4) hydrolysis of nitriles, and (5) reaction of Grignard reagents with CO2 (carboxylation). General reactions of carboxylic acids include (1) loss of the acidic proton, (2) nucleophilic acyl substitution at the carbonyl group, (3) substitution on the a carbon, and (4) reduction. 

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