Methyl ketals, reductive carbonylation

Acetaldehyde Production by Reductive Carbonylation of Methanol, Methyl Ketals, and Methyl Esters... 

Acetaldehyde is obtained from the reaction of synthesis gas with methanol, methyl ketals or methyl esters. The reactions are carried out with an iodide-promoted Co catalyst at 180-200 °C and 2000-5000 psig. In comparing the various feedstocks, the best overall process to make acetaldehyde involves the reductive carbonylation of methyl esters. In this case, acetaldehyde selec-tivities are > 95% ut acceptable rates and conversion. 

A carbonyl group cannot be protected as its ethylene ketal during the Birch reduction of an aromatic phenolic ether if one desires to regenerate the ketone and to retain the 1,4-dihydroaromatic system, since an enol ether is hydrolyzed by acid more rapidly than is an ethylene ketal. 1,4-Dihydro-estrone 3-methyl ether is usually prepared by the Birch reduction of estradiol 3-methyl ether followed by Oppenauer oxidation to reform the C-17 carbonyl function. However, the C-17 carbonyl group may be protected as its diethyl ketal and, following a Birch reduction of the A-ring, this ketal function may be hydrolyzed in preference to the 3-enol ether, provided carefully controlled conditions are employed. Conditions for such a selective hydrolysis are illustrated in Procedure 4. 

Ginsburg<29 31) took advantage of a preformed octahydrophenanthrene, 40 (Scheme 3.6). Conventional chemistry gave the ketal, 41, but an attempt to ketalize the free ring carbonyl caused cyclization to the trioxomorphinan, 42. Sequential reduction and N-methylation gave the previously described 4. 

The difficultly accessible trans-syn-trans arrangement of the a-b-c ring system present in steroidal antibiotics has now been synthesized. The known enedione (39) was converted into a 6 1 mixture of the desired compound (40) and its isomer (41) by ketalization of the saturated carbonyl, followed by lithium-ammonia reduction and enolate trapping with methyl iodide. After separation, (40) was converted into the tricyclic enedione (42) by standard procedures. The transfused AB-system was then obtained by ketalization, peracid treatment, and boron trifluoride rearrangement of the resulting epoxide to the keto-diketal (43). Removal of the 6-keto-group was performed under mild conditions by a new... 

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