Reagents tert- butyl acetate

Quite a number of other electron withdrawing groups containing multiple heteroatomic bonds, such as the ester carbonyl, nitrile, carboxamide, etc., can likewise stabilize carbanions. The lithium salt of tert-butyl acetate 32 is an example of an enolate anion sufficiently stable as a salt to be used as a shelf reagent. Substituents containing easily polarizable atoms, such as sulfur or selenium, are also capable of stabilizing an adjacent anionic center. 

Pseudo-/ -DL-gi Zopyranose triacetate (36) was prepared by hydroxyla-tion of the enetriol triacetate (32) and converted to the corresponding pentol and pentaacetate. The intermediate 32 was obtained by Diels-Alder reaction (200°C., two days) of rans/ rans-l,4-diacetoxy-l,3-buta-diene with allyl acetate. The double bond was surprisingly inert to the usual additive reagents and not detectable by infrared spectroscopy because of near-symmetry, but it did react with tert-butyl hydroxperoxide to give 36 in about 30% yield (27). 

Most of the subsequent work on this reagent was concerned with the formation of aryl radicals (see review by Cadogan, 1971). However, 2-terf-butyl-A-nitrosoacet-anilide was found to decompose in benzene to give, instead of 2-tert-butylbiphenyl, as expected for a substitution of benzene by a 2-tert-butylphenyl radical, a mixture of isomeric tert-butylphenyl acetates. A careful reexamination (Cadogan and Hib-bert, 1964) suggested that the ratio of 2- and 3-tert-butylphenyl acetates was consistent with the involvement of 2-tert-butylbenzyne, i.e., the product of an ionic dediazoniation, as an intermediate. This was later confirmed by trapping experiments designed to detect aryne intermediates. 

The earliest oxidations were effected with nitrous fumes and later with mercuric oxide and isoamyl nitrite.74 Lead tetraacetate in acetic acid is in many cases the reagent of choice, but the removal of by-products can present some difficulties.75 IV-Haloimides and amides in alcoholic solutions have been reported to yield essentially pure tetrazolium salts76 and have been found specially useful in the preparation of heteroaryl-substituted tetrazolium salt.77,78 The novel formazans 49 have been successfully oxidized to 50 using 7V-chloro succinimide (Eq. II).79 tert-Butyl hypo-... 

A variety of optically active 4,4-disubstituted allenecarboxylates 245 were provided by HWE reaction of intermediate disubstituted ketene acetates 244 with homochiral HWE reagents 246 developed by Tanaka and co-workers (Scheme 4.63) [99]. a,a-Di-substituted phenyl or 2,6-di-tert-butyl-4-methylphenyl (BHT) acetates 243 were used for the formation of 245 [100]. Addition of ZnCl2 to a solution of the lithiated phos-phonate may cause binding of the rigidly chelated phosphonate anion by Zn2+, where the axially chiral binaphthyl group dictates the orientation of the approach to the electrophile from the less hindered si phase of the reagent. Similarly, the aryl phosphorus methylphosphonium salt 248 was converted to a titanium ylide, which was condensed with aromatic aldehydes to provide allenes 249 with poor ee (Scheme 4.64) [101]. 

Toluene, dichloromethane, acetic acid, ammonium hydroxide, concentrated H2SO4, 5 N NaOH and 37% HCI were purchased from Mallinckrodt Inc. tetrahydrofuran, tert-butyl alcohol, anhydrous Na2S04, and NaCI were purchased from EM Science potassium tert-butoxide was purchased from Aldrich Chemical Company, Inc. hexanes was purchased from Baxter, and dry O2 was purchased from Air Products. All these reagents were used as received. 

Free cydohexene from peroxides by treating it with a saturated solution of sodium bisulphite, separate, dry and distil collect the fraction, b.p. 81-83°. Mix 8 2 g. of cydohexene with 55 ml. of the reagent, add a solution of 15 mg. of osmium tetroxide in anhydrous tert.-butyl alcohol and cool the mixture to 0°. Allow to stand overnight, by which time the initial orange colouration will have disappeared. Remove the solvent and unused cydohexene by distillation at atmospheric pressure and fractionate the residue under reduced pressure. Collect the fraction of b.p. 120 140°/15 mm. this solidifies almost immediately. Recrystallise from ethyl acetate The yield of pure cts-1 2-cydohexanediol, m.p. 96°, is 5-0 g. 

Schotten-Baumann type N-benzoylation was carried out on trans-4-hydroxy-L-proline 34,39 giving amide 43 in a satisfactory yield of 65%. The disappointing yield here could be attributed to difficulties experienced in recrystallization of the product 43. The amide 43 was esterified to give tert-butyl ester 44 using a modification of a procedure described by Widmer40 with dimethylformamide-dineopentyl acetal and tert-butanol as reagents. This provided crystalline 44 in 71% yield from 43 with no evidence of terf-butyl ether formation at the C-4 hydroxyl group (Scheme 12). 

The situation is similar with cyclic boronates, which are prepared by the following procedure. Steroid (10 pmol) and the respective substituted boric acid (10 jumol) are dissolved in ethyl acetate (1 ml) and the mixture is allowed to stand for 5 min at room temperature. Under these conditions, 17,20-diols, 20,21-diols and 17,20,21-triols are converted completely into boronates. Cyclic boronate was mainly produced from 17,21-dihydroxy-20-ketone, but side-products also appeared, the formation of which could be suppressed by adding a 10% excess of the reagent [387—389]. Different substituents on the boron atom, such as methyl, n-butyl, tert.-butyl, cyclohexyl and phenyl, are interesting from the viewpoint of GC—MS application. They are further suitable for converting isolated hydroxyl groups into TMS or acetyl derivatives. 

Commercial reagent-grade ethyl acetate was used as received. Ethyl acetate is best choice of solvent with regard to reaction time. Alcohols such as methanol or ethanol should be avoided because di-tert-butyl dicarbonate is decomposed by these solvents. 

The oxidation of acetate by peroxodisulphate is much slower than that of formate. Glasstone and Hickling showed that the products, which include carbon dioxide, methane, ethane, and ethylene, are similar to those produced by the anodic oxidation of acetate ions (Kolbe electrolysis), and they inferred that the same organic radicals are formed as intermediates. Similar results are reported by Eberson et al. for the oxidations of ethyl terf.-butyl-malonate, tert.-butyl-cyanoacetate, and ferl.-butyl-malonamate ions. The oxidations of these ions and of acetate by peroxodisulphate are first order with respect to peroxodisulphate and zero order with respect to the substrate. Mechanisms involving hydroxyl radicals are excluded because the replacement of peroxodisulphate by Fenton s reagent leads to different products, so Eberson et al. infer that the initial attack on the substrate is by sulphate radical-ions. Sengar and Pandey report that the rate of the silver ion-catalysed oxidation of acetate is independent of the peroxodisulphate concentration. 

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