Ozonolysis, abnormal

The suggested fragments from (54a) are a carbonyl compound (58) and a peroxy zwitterion (59), the latter then effecting a 1,3-dipolar addition on the former to yield the ozonide (57a). Alternative reactions of the zwitterion (59), including its polymerisation, lead to the formation of the abnormal products that are sometimes observed in addition to the ozonide, If ozonolysis is carried out in MeOH as solvent then (59) is trapped , as it is formed, by its conversion into the relatively stable a-hydroperoxy ether (60) ... 

The abnormal ozonolysis is chiefly observed when the group R is one that shows a high migration aptitude in carbonium ion rearrangements. 

In the ozonolysis of allylic compounds, varying amounts of products are formed that are due to cleavage of both the C=C double bond and the adjacent C—C single bond. These are the so called abnormal or anomolous products which arise from a fragmentation of the intermediate ozonide (59) (Scheme 10) <81TL1447>. 

In some cases, some abnormal products have been observed for example in the ozonolysis of allylic compounds [14] such as CH3CH=CH-CH2OH where formation of HCOOH is identified. 

Bailey and Colomb278 described an ozonolysis of 2,5-diphenylfuran in methanol-acetone, with two equivalents of ozone, which gave 14% phenylglyoxal and 81% benzoic acid. Abnormal ozonizations such as this can be explained if we consider that the initial step is the normal 2,5-addition of ozone on the furan ring. Then 26 or the primary ozonides 27 or 28 could give the resulting ketonic product ... 

New and continuing efforts towards the total synthesis of dendrobine (59 R = H) have been reported.In one sequence (Scheme 8), the butyric acid (85) was readily transformed into the ketal (86), which was submitted to a Birch reduction and hydrolysis to yield the cyclohexenone (87) as the single diastereomeric product. Acid treatment of (87) gave a stereoisomeric mixture of products (88) which were not separated but subjected to reaction with base to give compound (89). The same compound was obtained directly by treatment of (87) with strong base (Michael and aldol condensations combined). After some discouraging results, the tricyclic compound (89) was transformed into the desired keto-acid (90) via an abnormal ozonolysis reaction. Compound (90) possesses the correct stereochemistry at three asymmetric centres required for elaboration of dendrobine (59 R = H). 

Ozone acetic acid Ketocarboxylic acids by abnormal ozonolysis... 

Abnormal imidazolylidene ruthenium complex 45 was developed by Bera and co orkers for the NaI04-mediated oxidation of olefins as a mild alternative to ozonolysis [eqn (3.9)]. For example, styrene was oxidized to benzaldehyde quantitatively in half an hour at room temperature with only 1 mol% 45. Internal olefins were oxidized very efficiendy as well, and cyclic olefins such as cyclohexene afforded a,o)-dialdehydes in excellent yields. Traces of over-oxidation to the corresponding carboxylic acids were only observed with aliphatic olefins. Also,... 

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