Carbonyl functional groups hydrolysis

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. 

Under basic conditions, the o-nitrotoluene (5) undergoes condensation with ethyl oxalate (2) to provide the a-ketoester 6. After hydrolysis of the ester functional group, the nitro moiety in 7 is then reduced to an amino function, which reacts with the carbonyl group to provide the cyclized intermediate 13. Aromatization of 13 by loss of water gives the indole-2-carboxylic acid (9). 

A variant on this theme contains mixed acyl groups. In the absence of a specific reference it may be speculated that the synthesis starts with the diacetyl derivative (15). Controlled hydrolysis would probably give the monoacetate (16) since the ester para to the ketone should be activated by that carbonyl function. Acylation with anisoyl chloride followed by reduction would then afford nisobuterol (18). 

The utilization of benzothiazole as a carbonyl synthon, in a process that involves the intermediacy of the benzothiazole-2-anion, was discussed in Section III,C,4, but in addition, by a closely related process, the same species can also be used as a protecting group for the carbonyl function (85H2467 91BCJ3256). This protective role is the same as that found earlier for 1-methylimidazole (Scheme 153) (84TL3251), with deprotection involving a quaternization step, which is then followed by basic hydrolysis. 

Amino acids are the building blocks of proteins. A single protein consists of one or more chains of amino adds strung end to end by peptide bonds Hence the name polypeptide. You must be able recognize the structure of an amino acid and a polypeptide. A peptide bond creates the functional group known as an amide (an amine connected to a carbonyl carbon). It is formed via condensation of two amino acids. The reverse reaction is the hydrolysis of a peptide bond. 

Carboxylic acids are easily converted to a variety of acid derivatives. Each derivative contains the carbonyl group bonded to an oxygen or other electron-withdrawing element. Among these functional groups are acid chlorides, esters, and amides. All of these groups can be converted back to carboxylic acids by acidic or basic hydrolysis. 

The nitroso compound is unstable because it can tautomerize with the transfer of a proton from carbon to the oxygen of the nitroso group. This process is exactly like enolization but uses an N=0 instead of a C-O group. It gives a more familiar functional group from Chapter 14, the oxime, as the stable enol . The second structure shows how the oxime s O-H can form an intramolecular hydrogen bond with the ketone carbonyl group. Hydrolysis of the oxime reveals the second ketone. 

---