Carbamates sulfonylation

Sulfonamides (R2NSO2R ) are prepared from an amine and sulfonyl chloride in the presence of pyridine or aqueous base. The sulfonamide is one of the most stable nitrogen protective groups. Arylsulfonamides are stable to alkaline hydrolysis, and to catalytic reduction they are cleaved by Na/NH3, Na/butanol, sodium naphthalenide, or sodium anthracenide, and by refluxing in acid (48% HBr/cat. phenol). Sulfonamides of less basic amines such as pyrroles and indoles are much easier to cleave than are those of the more basic alkyl amines. In fact, sulfonamides of the less basic amines (pyrroles, indoles, and imidazoles) can be cleaved by basic hydrolysis, which is almost impossible for the alkyl amines. Because of the inherent differences between the aromatic — NH group and simple aliphatic amines, the protection of these compounds (pyrroles, indoles, and imidazoles) will be described in a separate section. One appealing proj>erty of sulfonamides is that the derivatives are more crystalline than amides or carbamates. 

Inclusion of a para acetyl group requires a somewhat different approach to the preparation of these compounds. Reaction of the diazonium salt from p-aminoacetophenone with sulfur dioxide affords the sulfonyl chloride, 203 this is then converted to the sulfonamide, 204, Elaboration via the carbamate with cyclohexyl-amine affords acetohexamide (205). ... 

The most important group of derivatives for the amino function (Fig. 7-4) is the carbamate group, which can be formed by reactions with acids, acid chlorides or acid anhydrides. A series of chlorides as 2-chloroisovalerylchloride [1], chrysanthe-moylchloride [2] and especially chloride compounds of terpene derivatives (cam-phanic acid chloride [3], camphor-10-sulfonyl chloride [4]) are used. The a-methoxy-a-trifluoromethylphenylacetic acid or the corresponding acid chloride introduced by Mosher in the 1970s are very useful reagents for the derivatization of amines and alcohols [5]. 

Method C From Ethyl N- [(4-N itrophenyl)sulfonyl]oxy carbamate 3 5... 

CN [(lS,2/ )-3-[[(4-Aminophenyl)sulfonyl](2-methylpropyl)amino]-2-hydroxy-l-(phenylmethyl)propyl]carbamic acid (3S)-tetrahydro-3-furanyl ester... 

CN [3-[[2-methoxy-4-[[[(2-methylphenyl)sulfonyl]amino]carbonyl]phenyl]methyl]-l-methyl-lH-indol-5-yl]carbamic acid cyclopentyl ester... 

Al-(Alkoxycarbonyl) 0-(arenesulfonyl)hydroxylamines [alkyl Af-(arenesulfonyloxy) carbamates] 3i-o can be easily obtained by sulfonylation of commercially available iV-(alkoxycarbonyl)hydroxylamines (alkyl V-hydroxy carbamates). Af-(Alkoxycarbonyl) hydroxylamines can be also prepared from hydroxylamine and alkyl chloroformate . ... 

Complete regiodirection by the NHCOOR for 4-sulfurated (sulfenyl, sulfmyl, and sulfonyl) -1,3-butadiene-1 -carbamates in their Diels-Alder reactions [182] is quite natural. The case at issue might be the sulfenylated compounds, but we must remember that divalent sulfur can act as an acceptor. 

While the use of acyl and sulfonyl protecting groups led to mediocre yield, masking of the nitrogen in the form of a carbamate led to improved yields.15... 

The Curtius rearrangement provides a route to carbamates of a-amino sulfonamides (Scheme 25). 108 Reaction of the ethyl ester of an a-bromo acid 52 with Na2S03 yielded the sodium salt of the corresponding sulfonic acid 53. Treatment of 53 with PQ5 afforded the sulfonyl chloride 54 which on reaction with an amine gave the sulfonamide 55. The latter... 

Support-bound /V-sulfonyl carbamates, which can be prepared by N-sulfonylation of resin-bound carbamates, are susceptible to nucleophilic cleavage. These intermediates enable the solid-phase preparation of A-ary I- or /V-alkylsulfonamides using inexpensive hydroxymethyl polystyrene (Entries 8 and 9, Table 3.15). Polystyrene-bound carbamates can also be cleaved by treatment with acyl halides in the presence of Lewis acids (Entry 4, Table 3.16). 

Alternatively, sulfonamides can also be prepared by oxidation of sulfinamides with periodate (Entry 3, Table 8.8) or with MCPBA [125]. Polystyrene-bound sulfonyl chlorides, which can be prepared from polystyrene-bound sulfonic acids by treatment with PCI5, SOCI2 [126-129], CISO3H [130], or SO2CI2/PPI13 [131], react smoothly with amines to yield the corresponding sulfonamides (Entry 4, Table 8.8). Support-bound carbamates of primary aliphatic or aromatic amines can be N-sulfonylated in the presence of strong bases, and can therefore be used as backbone amide linkers for sulfonamides (Entries 5 and 6, Table 8.8). 

Since BAs occurring in food do not exhibit satisfactory absorbance or fluorescence in the visible or ultraviolet range, chemical derivatization, either pre- (35-37) or postcolumn (38), is usually used for their detection in HPLC. The most frequently employed reagents for precolumn derivatization are fluorescamine, aminoquinolyl-lV-hydroxysuccinimidyl carbamate (AQC) (39, 40), 9-fluorenylmethyl chloroformate (FMOC) (41-43), 4-dimethylaminoazobenzene-4 -sul-fonyl chloride (dabsylchloride, DBS) (44), N-acetylcysteine (NAC) (45,46), and 5-dimethyl-amino-1-naphthalene-1-sulfonyl chloride (dansylchloride, DNS) (47,48), phthalaldehyde (PA), and orf/to-phthaldialdehyde (OPA) (49-51), together with thiols such as 3-mercaptopropionic acid (MPA) (37) and 2-mercaptoethanol (ME) (35,49). 

Bromocyclization of the thiocarbamidate generated from f-butylisothiocyanate and 3-buten-2-ol gave oxazolidinone products with slight selectivity for the cis isomer (cis.trans 1.9 1),2271 while iodocycliza-tions of /V-sulfonylated carbamates gave somewhat higher stereoselectivity (equation 117).233... 

Using / -nitrobenzene sulfonyl carbamates as the source of nitrene, the reaction needs to be activated either by a carbonate in the presence of phase-transfer reagent or by sonication. Yields are only moderate and this reaction cannot be regarded as being preparatively useful.101,102... 

Epoxidation of A-ZW-butylsulfonyl-1,2,3,6-tetrahydropyridine 236 followed by addition of alkyllithium reagents gives a mixture of allylic alcohols 237 and 4-hydroxy-1,2,3,4-tctrahydropyridines 238 (Equation 21) <2003T9729>. Exchange of the A-sulfonyl group for a carbamate results in formation of tetrahydropyridines 238 and little or no allylic alcohol is formed. 

The simplest 1,3-dipolar cycloadditions of diazomethane were presented in Figure 15.36. Diazomethane is generated from sulfonamides or alkyl carbamates of A-nitrosomethylamine. The preparation shown in Figure 15.40 is based on the commercially available />ara-toluene-sulfonylmethylnitrosamide (Diazald ). In a basic medium, this amide forms a sulfonylated... 

In contrast to stereoselective C-C bond-forming reactions, the related electrophilic animation of chiral carbon nucleophiles is a recent conceptual advance in the repertoire of synthetic methodology. The problem is the correct choice of the nucleophile, and of the most efficient nitrogen electrophile. The chemistry of useful reagents such as sulfonyl azides 3 and chloro nitroso alkanes 5 was excellently reviewed in 1995 [Id]. This chapter outlines a collection of the major reports that have appeared in the field of stereoselective electrophilic animation using sulfonyloxy-carbamates 6 and azodicarboxylates 4. 

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