Sulfonyl with carbamates

Exocyclic a,P-unsaturated lactones (e.g. 137) have been converted to the corresponding spiroaziridines 138 by treatment with ethyl AT- [(4-nitrobenzene)sulfonyl]oxy carbamate (Ns0NHC02Et) in the presence of caleium oxide <03TL4953>. In a similar vein, a novel chiral carbamate 139 based on Helmchen s alcohol has been applied to the same conditions with moderately good diastereoselectivities, as shown in the aziridination of carboethoxy-cyclopentenenone 140 <03TL3031>. 

Aziridine-2-phosphonates spiro-fused with 2-oxindole (790) have been prepared by a straightforward Horner-Wadsworth-Emmons reaction of ethyl 7V- [(4-nitrophenyl)sulfonyl]oxy -carbamate (791) and 3-(phosphoryl-methylene)oxindoles (792) in the presence of calcium oxide. Oxindoles (792) were also transformed into novel oxirane-2-phosphonates (793), as oxygen analogues of (790), by reaction with H202/Na0H (Scheme 201). " Cinchonine-based thiourea (797) catalysed asymmetric Michael addition of simple p-oxo-alkyl phosphonates (794) to nitro olefins (795), which afforded valuable a-substituted p-oxo phosphonates (796) in satisfactory yields with good to excellent enantioselectivities (up to 98% ee) (Scheme 202). ... 

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]. 

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... 

Reactions of organozinc reagents, prepared from organomagnesium compounds in situ (see Section 16), with a-sulfonyl ethers and carbamates [40] can give excellent results, e.g. [41]. 

A similar principle has been utilized with protecting groups, which are cleaved by nucleophilic attack to a Michael system forming an enolate that subsequently eliminates the carbamate anion. Protecting groups following this principle are 2-(ferf-butylsulfonyl)allyl-oxycarbonyl (30),t l l,l-dioxobenzo[h]thien-2-yhnethoxycarbonyl (31),t l and 2-(methyl-sulfonyl)-3-phenylallyloxycarbonyl (32)P 1 (Scheme 8). 

Protection of the Trp side chain in Fmoc synthesis is not always essential. However, if it is in close proximity to an Arg in the sequence where sulfonyl-based protection is employed then protection of the indole nitrogen with Boc is often recommended. This eliminates the back addition of the sulfonyl-based protecting group since the indole is protected as a carbamic acid during the TFA treatment. Exposure to mildly acidic aqueous conditions releases the free indole nucleus. 

The reagent reacts with alcohols and phenols to give urethane-N-sulfonyl chlorides, which are hydrolyzed by water to carbamates. It reacts with an olefin to give either a... 

---