Tert-butyl carbamate

In sharp contrast, Bartoli showed that the (salen) Co catalyst system could be applied to the kinetic resolution of terminal epoxides with unprotected tert-butyl carbamate as nucleophile with extraordinarily high selectivity factors (Scheme 7.40) [72]. Excellent yields and selectivities are also obtained with use of ethyl, Cbz,... 

For the use of tert-butyl carbamates, see Beak, R Lee, W. Tetrahedron Lett., 1989, 30, 1197. 

In a 50 mL round-bottomed flask equipped with a magnetic stirrer bar were placed tert-butyl carbamate (545 mg) and n-propanol (6 mL). A solution of sodium hydroxide (183 mg) in water (12.2 mL) and tert-butyl hypochlorite (0.53 mL) were added to the solution. The resulting solution was stirred for 5 minutes and cooled to 0°C. Then a solution of DHQ2PHAL (71 mg) in n-propanol (6mL), a solution of 4-methoxystyrene in //-propanol (12.2 mL) and potassium osmate dihydrate (22.5 mg) were added sequentially to give a green solution. After 1 hour at 0 °C, the reaction mixture had turned from green to yellow. 

The deprotection of t-Boc proline ester 2a is representative of the general procedure employed, tert-Butyl carbamate (0.217 g, 1.0 mmol) and aluminium chloride (0.134 g, 1.0 mmol) doped on a neutral alumina (1.0 g) were mixed thoroughly on a vortex mixer. The reaction mixture was placed in an alumina bath inside an unmodified household microwave oven (operating at frequency 2450 MHz) and irradiated for a period of 1 min. After completion of the reaction (monitored by TLC, EtOAc-hexane, 9 1 v/v), it was neutralized with aqueous sodium bicarbonate solution and the product was extracted into ethyl acetate (2x15 mL). The ethyl acetate layer was separated, dried over magnesium sulfate, filtered, and the crude product thus obtained was purified by column chromatography to afford pure methyl ester 2b in 88% yield. 

Fig. 6.38. Mechanism of the preparation of an isocyanate by acylation of anilines with tert-butyl dicarbonate in the presence of 4-(dimethylamino)pyri-dine. In the absence of this additive a tert-butyl carbamate would be produced instead of an isocyanate (cf. Figure 6.37.)...

The scope of the aromatic C-N bond formation extends beyond simple amine substrates. For example, selected imines, sulfoximines, hydrazines, lactams, azoles, carbamates, and amides all give useful products following aromatic C-N bond formation. In addition, allyl-amine undergoes arylation, providing an alternative to the ammonia surrogates benzyl-amine, tert-butyl carbamate, and benzophenone imine. Although it is an amine substrate, the reaction of this reagent is included here because of its special purpose. 

Prior to the recent paper by Buchwald, an intermolecular version of the arylation of carbamates was published by Hartwig et al. (Eq. (22)) [163]. His group showed that reactions catalyzed by a combination of Pd(OAc)2 and P(tBu)3 formed N-aryl carbamates from aryl bromides or chlorides and tert-butyl carbamate, but that this system was inactive for reactions of amides or sulfonamides. Again, the reaction conditions were not as mild as those used for animation, but they were similar to those employed in the reactions with Xantphos. For the intermolecular reactions, the use of sodium phenoxide as base was crucial. 

In peptide synthesis functional groups in the amino acid side chains are often protected with acid-labile protecting groups (Section 4.5.3). The tripeptide in Figure 4.35 contains, for example, a serine ferf-butyl ether and an L-lysine e-protected as an O-tert-butyl carbamate. In the standard strategy of synthesizing oligopeptides from the C- to the N-terminus (cf. Section 6.4.3) the C-terminus is either connected to the acid-labile... 

The tert-butyl carbamate ester of 4-amino-1,2-dimethoxybenzene (veratrylamine) was lithiated with n-butyllithium and carboxylated regiospedfically to afford a combined 70% yield of the 3- and the 5-carboxylic acids (20 1) while with... 

Docetaxel differs from paclitaxel at two positions in its chemical structure. It has a hydroxyl functional group on C-10 (see Fig. 101.1) whereas paclitaxel has an acetate ester, and a tert-butyl carbamate ester exists on the phenylpropionate side chain instead of the benzyl amide in paclitaxel. The C-10 functional group change causes docetaxel to be more water soluble than paclitaxel. 

The first total synthesis of the intricate Stemona alkaloid (+ /—)-isostemofoline (224) was reported by Kende and coworkers 81) starting from 1,2-hexanediol (225) which was straightforwardly converted to 227 (Scheme 22) 82). Reductive cycUzation with sodium hydrosulfite in refluxing aqueous ethanol, and protection of the unstable pyrrole as tert-butyl carbamate, afforded 228 in five steps with 12% overall )deld. The key bicyclic ketone 231 was assembled by [4 + 3] cycloaddition of pyrrole 228 and diazoester 229 promoted by rhodium octanoate dimer, followed by enol silane deprotection, exo-specific hydrogenation, and nucleophilic decarboxylation (47% overall yield). Sodium methoxide-catalyzed aldol condensation of ketone 231 and furfural provided the Q-j/i-unsaturated ketone 232 whose olefin configuration was established by nOe studies. Allylation of 232 provided a 2.4 1 mixture of ketone 234 and the corresponding allylic enol ether 233, which could be converted to the former via a stereoselective Claisen rearrangement. 

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