Alkene cleavage syntheses

The dibranched glycoside 62 from which the C18-C23 subunit of macrolide lasonolide A (63) can be obtained was prepared in several steps from 60 (see Chapter 14 for synthesis) via epoxide 61. Axial epoxide opening with LAH followed by oxidative alkene cleavage and reduction converts 61 to 62. ... 

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). 

We ve already discussed two methods of aldehyde synthesis oxidation of primary alcohols and oxidative cleavage of alkenes. 

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. 

Platinum (II) carbenes should be mentioned as <7-bonded organometallics. An important general synthesis by cleavage of an electron-rich alkene affords a pair of isomers, the trans-form isomerizing to the thermodynamically more stable cw-form on heating (Figure 3.61). 

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