Ozonolysis of an alkene

Ozone adds to the alkene to form an initial ozonide. 

Write the structures of the alkenes that would yield the following carbonyl compounds when treated with ozone and then with dimethyl sulfide. 

0 Alkynes show the same kind of addition reactions with chlorine and bromine that alkenes do. 

It is usually possible to prepare a dihaloaUcene by simply adding one molar equivalent of the halogen  

Addition of bromine to acetylenedicarboxylic acid, for example, gives the trans isomer in 70% yield  

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The oxidation of an alkene with ozone followed by treatment with zinc in the presence of acid gives aldehydes and/or ketones. The reaction breaks the carbon-carbon double bond and changes each of carbon atoms of the C=C to a carbonyl group. Figure 10-7 shows an excimple of the ozonolysis of an alkene. 

The ozonolysis of an alkene to form a ketone, and, in this case, an aldehyde. 

One of the key steps in the synthesis of the depsipeptide jasplakinolide involved the preparation of an aldehyde 273 by ozonolysis of an alkene 271 with the correct stereochemistry of the substituents (Scheme 83). The hydroxyl group was protected with R = fer7-butyl(dimethyl)silyl <2004ASC855>. 

Oxidation of an Alcohol- Section 10.14 Figure 10.8 Oxymercuration-Reduction Section 11.6 Figure 11.5 Ozonolysis of an Alkene Section 11.11... 

To predict the products from ozonolysis of an alkene, erase the double bond and add two oxygen atoms as carbonyl (C=0) groups where the double bond used to be. 

Ozonolysis can be used to determine the structure of an unknown alkene. If you know what carbonyl compounds are formed by ozonolysis, you can mentally work backward to deduce the structure of the alkene. For example, if ozonolysis of an alkene followed by a work-up under reducing conditions forms acetone and butanal as products, you can conclude that the alkene was 2-methyl-2-hexene. 

Ozonolysis of an alkene produces equal amounts of acetone and formaldehyde, (CH3)2C=0 and CH2=0, respectively. Deduce the alkene structure. 

Oxidation of a 2° alcohol produces a ketone, while partial oxidation of a 1° alcohol (PCC or Swem) gives aldehyde products. Ozonolysis of an alkene, followed by a reductive workup, gives ketone and/or aldehyde products, depending on the alkene starting material. Esters, acid chlorides, and nitriles can be partially reduced with diisobutylaluminum hydride (DIBAL-H) to produce aldehydes as well. 

If the size of the carbon skeleton decreases, then a C—C bond-breaking reaction, called bond cleavage, is required. Once again, we have only seen one such reaction. Ozonolysis of an alkene (or aUtyne) achieves bond cleavage at the location of the Tt bond ... 

Ozonolysis of an alkene, followed by treatment with dimethyl sulfide, forms the following product(s). Identify the alkene in each case. 

At this point in your study of organic chemistry, you know only three ways to synthesize a ketone (1) the addition of water to an alkyne (Section 7.7), (2) hydroboration-oxi tion of an alkyne (Section 7.8), and (3) ozonolysis of an alkene (Section 6.12). Because the target molecule has the same number of carbons as the starting material, we can rule out ozonolysis. Now we know that the precursor molecule must be an alkyne. The alkyne needed to prepare the ketone can be prepared from two successive E2 reactions of a vicinal dihahde, which in turn can be synthesized from an alkene. The desired alkene can be prepared from the given starting material by an elimination reaction, using a bulky base to maximize the elimination product... 

When you know what functional group you want to create, you can try to remember the various ways it can be synthesized. For example, a ketone can be synthesized by the acid-catalyzed addition of water to an alkyne, hydroboration-oxidation of an alkyne, oxidation of a secondary alcohol, and ozonolysis of an alkene. Notice that ozonolysis decreases the number of carbons in a molecule. 

DMS Ozonolysis Ozonolysis of an alkene causes cleavage of the C=C bond, giving two compounds, each of which possesses a C=0 bond. 

However, after installing two carbon atoms, we can remove one of them with an ozonolysis procedure. In order to obtain an aldehyde, the last step must be ozonolysis of an alkene, so the second-to-last step (called the penultimate step) must be reduction of the alkyne to an alkene in the presence of a poisoned catalyst ... 

The starting material has one more carbon atom than the product. Therefore, our synthesis must employ an ozonolysis process. Since the product is a carboxyhc acid (rather than an aldehyde or ketone), we can conclude that the last step of our process must involve ozonolysis of an alkyne, rather than ozonolysis of an alkene ... 

Thus far, we have learned two ways to make aldehydes (i) a/ift-Maikovnikov hydration of a terminal alkyne or (ii) ozonolysis of an alkene, either of which is potentially reasonable here. However, in order to produce botii of these compounds from a single synthetic protocol, a key recognition is that they can be produced fiom ozonolysis of the following (hsubstituted alkene. 

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