Tert carbonic anhydride

Azotomycin is anticancer antibiotic produced by Streptomyces ambofaciens. Total sythesis of it from y-benzyl-N-tert-butyloxycarbonyl-L-glutamic acid (y-OBzi-N-Boc-L-Glu) has been accomplished in nine steps. The mixed carbonic anhydride method was chosen for peptide bond formation. Commerically available y-OBzi-N-Boc-L-Glu was esterified with ethereal diazomethane, deprotected with trifluoroacetic acid-methylene chloride (1 1), and converted to hydrochloride y-benzyl-L-glutamic acid a-methyl ester (y-OBzi-L-Glu-a-OMe HCI) by treatment with dry hydrogen chloride in ethyl ether, MP 129°-135°C (dec.) [a]D25= + 13.3° (CHCI3). 

The reaction of 2 equivalents of tert-butyl dicarbonate with A -Z-protected amino acids in tBuOH and catalytic DMAP (0.1 equiv) proceeds smoothly over 30 minutes to give the corresponding esters in high yields (see Section 3.9.3.2).P Preparation of tert-butyl esters of N-protected anoino acids via tert-butyl mixed carbonic anhydride generated in situ by reaction with tert-butyl fiuorocarbonate has been reported by Loffet et al.t l Finally, N -Z-protected amino acids are esterified in good yields with tert-butyl bromide.P ... 

More recently tert.butyl pyrocarbonate, usually described as tert.butyl carbonic anhydride, gained considerable popularity, mainly because the products formed during introduction of the Boc group, are harmless and easily removed ... 

There are many electrophiles which not only terminate living polymer chains but also produce end-group substitution. For example, macromolecules with hydroxyl, carboxyl, thiol, or chlorine termini can be prepared by reacting living polymers with such compounds as epoxides, aldehydes, ketones, carbon dioxide, anhydrides, cyclic sulfides, disulfides, or chlorine (15-23). However, primary and secondary amino-substituted polymers are not available by terminations with 1° or 2° amines because living polymers react with such functionalities (1.). Yet, tert-amines can be introduced to chain ends by use of -N-N-di-methylamino-benzaldehyde as the terminating agent (24). 

Fig. 6. 35. Preparation of the dicarbonate ("pyrocarbonate") H ("Boc anhydride," "Boc20") from potassium tert-butoxide, carbon dioxide and phosgene. The tricarbonate E is isolated as an intermediate. Only upon addition of a catalytic amount of the nucleophilic amine F does E react to afford Boc 0, while the analogous ethyl derivative ofthe tricarbonate does so spontaneously. Boc20 applications are shown in Figures 6.37 and 6.38, an application ofthe analogous diethyldicarbonate is given in Figure 13.62.

By retro synthetic analysis collagenase inhibitor RO0319790 (1) can be assembled from two chiral building blocks, (R) -succinate 2 and (S)-tert-leucine N-methyla-mide 13. As the latter can be prepared from commercially available (S)-tert-leucine 8 our work concentrated in particular on the construction of the first building block 2. In order to assemble the carbon skeleton of 2 in the most efficient way, extremely cheap maleic anhydride 4 was converted in a known ene reaction with isobutylene to provide the cyclic anhydride 6. Hydrogenation of the double bond followed by the addition of EtOH/p-TsOH yielded the racemic diethyl ester substrate 9 for the enzyme reaction. The enzymatic monohydrolysis of 9 afforded the monoacid (R)-2a. (R)-2 a was coupled via its acid chloride with leucine amide 13 to ester 14, which finally was converted into the hydroxamic acid 1. 

Cyclopentenediol isomers have previously been prepared by hydrolysis of acetates produced by reaction of dibromocyclopen-tene with potassium acetate in acetic acid 2 by reaction of cyclo-pentene with selenium dioxide in acetic anhydride or by reaction of cyclopentadiene with phenyl iodosoacetate,4 with lead tetraacetate,6 or with peracetic acid in the absence of base. Preparation of cyclopentenediol without intermediate formation of acetates has been accomplished by reaction of cyclopentadiene with hydrogen peroxide in the presence of osmium tetroxide in tert-butanol,7 and by reaction of cyclopentadiene with peracetic acid in a methylene chloride suspension of anhydrous sodium carbonate, followed by hydrolysis of the resulting epoxycyclopen tene.8... 

NITRATE de ZINC (French) (7779-88-6) Noncombustible, but will enhance the combustibility of other materials. Many chemical reactions can cause fire and explosions. A strong oxidizer. Violent reaction with reducing agents, strong oxidizers, combustible materials, organic substances, metallic powders, acetic anhydride, tert-butylhydroperoxide, carbon, dimethylformamide, metal cyanides, metal sulfides, phosphorus, sodium acetylide, sulfur, thiocyanates. Incompatible with amines, ammonium hexacyanoferrate(II), boranes, cyanides, citric acid, esters, hydrazinium perchlorate, isopropyl chlorocarbonate, nitrosyl perchlorate, organic azides, organic bases, sodium thiosulfate, sulfamic acid. Attacks metals in the presence of moisture. 

For the formation of nitro derivatives mild conditions are essential to avoid replacement of the branched alkyl group (ref. 88). The nitration of 6-tert-butyl-3-methylphenol and methylation of the product 6-tert-butyl-2,4-dinitro-3-methylphenol in xylene containing potassium carbonate with dimethyl sulphate offers an alternative to the classical route for musk ambrette. Hazards can be involved in this more well-known procedure consisting of the nitration of 6-tert-butyl-3-methylanisole (ref. 89) in acetic anhydride. 

Im Gegensatz dazu liefert die Ozonolyse von z. B. (tert.-Butylthio-carbonyl)-cyclohexan das gemischte Carbonsaure-Sulfonsaure-Anhydrid (75%)257, das hydrolytisch zu Carbon-saure und Sulfonsaure gespalten werden kann258 ... 

---