Alkenes, cyclic => dialdehydes

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

Trans -substituted diarylalkenes undergo oxidative cleavage upon treatment by potassium permanganate in the presence of moist alumina as a solid support (equation 32)158. Under the same conditions, cyclic alkenes, with medium-sized rings, give acyclic dialdehydes (equation 33). 

Oxidation with ozone is a common method for the preparation of fluorinated compounds. Cyclic or linear alkenes can be treated with ozone and, depending on the workup of the reaction mixture, aldehydes, ketones or carboxylic acids are produced. This is illustrated by the ozonoly-sis of. l,.3,4.4-tetrafluorocyclohexene. Oxidative workup gives, depending on the oxidizing agent, formylpentanoic acid 3 or the diaeid 4 with reductive workup the dialdehyde 2 is obtained. If the alkene is substituted by an alkyl group, the product is a ketone. 

Ozonolysis of a cyclic alkene leads to oxidative cleavage, but the two carbonyl fragments are connected, so there is only one product rather than the two observed from ozonolysis of 2,3-dimethyl-2-butene or 2-methyl-2-pentene. When cycloheptene, for example, is treated with ozone and then with zinc and acetic acid, oxidative cleavage leads to the a,(o-dialdehyde 146 (1,7-heptanedial or 1,7-heptanedicarboxaldehyde). 

The ozonolysis of cyclic alkenes in protic solvents followed by reductive decomposition of the hydroperoxides formed is a classical method for dialdehydes synthesis [70], This method is applied for the preparation of 3-ethoxycarbonylglutaric dialdehyde by ozonolysis of ethyl 3-cyclo-pentenecarboxylate. The dialdehyde is an intermediate in the sjmthesis of dolazetrone mesitilate, which is an active medical substance in AN-ZEMET anti-emetik. Zn/AcOH, phosphines, amines and sulfides such as 3, 3 -thiodipropionic acid and its salts are the most suitable redactors for this system. Their efficiency is comparable to that of methyl sulphide but without its shortcomings. The polymer immobilized 3,3 -thiodipropionic acid is also very active in this reduction reaction [70]. 

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