Protecting group carbamate

To minimize racemization, the use of nonpolar solvents, a minimum of base, low reaction temperatures, and carbamate protective groups (R = O-alkyl or O-aryl) is effective. (A carbamate, R = O-r-Bu, has been reported to form an oxazolone that appears not to racemize during base-catalyzed coupling.) ... 

To minimize racemization, the use of nonpolar solvents, a minimum of base, low-reaction temperatures, and carbamate protective groups (R = O-alkyl or O-aryl) are effective. 

Comparison of Cleavage Rates for Various Carbamate Protective Groups... 

Another carbamate protecting group is 2,2,2-trichloroethyoxycarbonyl, known as Troc. 2,2,2-Trichloroethylcarbamates can be reductively cleaved by zinc.220... 

The major problems with industrial-scale applications of this procedure are the use of expensive reagents, the required chromatographic separation of the side products and the competitive formation of oxazolines. The use of carbamate protecting groups avoided the oxazoline problem and is usually preferred, since the resulting protected 3-amino-substituted /3-lactams 150 can later be deprotected and reacylated. 

Compounds in this dibenzocycloheptene series also manifest antidepressant activity when the trigonal one-carbon bridge is replaced by tetrahedral carbon. Thus, the reaction of hydrocarbon (24-7) with a metal amide in liquid ammonia leads to the corresponding carbanion (29-1). Treatment of that with the ethyl carbamate from A -methyl-3-chloropropylamine (29-2) leads to the alkylation product. The carbamate protecting group is then removed by sequential saponification with a base followed by acidification. This yields the antidepressant agent protriptyline (29-3) [30]. 

Like Cbz, the f-Boc group is a carbamate protecting group. But, unlike Cbz, it can be removed simply with dilute aqueous acid. Just 3M HCl will hydrolyse it, again by protonation, loss of f-butyl cation, and decarboxylation. 

Functionalization of the bridgehead 2-position in benzomorphans by standard synthetic approaches is not easy. This led Portoghese and Ramakrishnan(117) to devise a new 2-tetralone synthesis from a conventional benzomorphan Hofmann elimination product (185). Demethylation of 185 was effected by trichloroethylchloroformate to 186, which, in turn, was oxidized to the 2-tetralone (187). Removal of the trichloroethyl carbamate protecting group gave 189, presumably via 188. Treatment of 189 with KCN in weak... 

Carbamate (urethane) protecting groups The best amino group protection is carried out by the formation of the urethane (or carbamate) protecting groups. Carbamates are... 

Reduction of the a,p-unsaturated ester 21 with LiAlH4 and subsequent removal of the carbamate protection group provides minfiensine (1) in 85 % yield over two steps. 

Transformation of 1,3-diamino-2-propanol (144) into vicinal diamines has been reported. Thus, the bis(benzyloxycarbonyl) derivative of (144) was mesylated to give (145), which was converted into 1-benzyloxycarbonylaziridine (146). Acetic acid and HCl reacted at the ring carbon of (146) affording 2,3-diamino-1-propanol (147) and l-chloro-2,3-diaminopropane (148 Scheme 68). On the other hand, the reaction of (146) with Grignard reagents and sodio malonates resulted in the loss of the carbamate protecting group. In contrast, the sulfonamide derivative (149) could be converted into diamines (151) and (152) via 1-tosylaziridine (150 Scheme 68). 

Reduction of the carbamate-protecting group by the action of LiAlH4 afforded 742b in 92% yield. An acid-mediated hydrolysis of the silyl ether provided ( + ) -dehydrocuscohygrine (743) in 89% yield. Further oxidation of the alcohol under Jones conditions produced the desired target 744 in 73% yield. 

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