Amines cyanohydrin acetates

The vindoline synthesis required prior preparation of the amine coupling partner, the 2,4-dinitrobenzenesulfonamide 713, which was prepared from the pent-anal 710, as shown in Scheme 43. A notable feature of this route was the enzyme-mediated resolution of the cyanohydrin acetate 711, via enzymatic hydrolysis to selectively afford a diastereomeric mixture of only the (5)-cyanohydrins 712. 

Drop-hydrogenation—Amines from cyanohydrin acetates and from 1,1-nitroethylene derivatives s. 13, 79... 

Catalytic hydrogenation of the nitrile function of cyanohydrins can give amines. As in the case of ordinary nitriles, catalytic reduction of cyanohydrins can yield a mixture of primary, secondary, and tertiary amines. Addition of acid or acetic anhydride to the reaction medium minimizes formation of secondary or tertiary amines through formation of the amine salt or acetamide derivative of the primary amine. 

Aldehydes, ketones, and acetals react with allyltrimethylsilane in the presence of a catalytic amount of BiX3 (X = C1, Br, OTf) to give homoallyl alcohols or homoallyl alkyl ethers (Equation (52)).91-93 The BiX3-catalyzed allylation of aldehydes and sequential intramolecular etherification of the resulting homoallylic silyl ethers are involved in the stereoselective synthesis of polysubstituted tetrahydropyrans (Equation (53)).94,95 Similarly, these Lewis acids catalyze the cyanation of aldehydes and ketones with cyanotrimethylsilane. When a chiral bismuth(m) catalyst is used in the cyanation, cyanohydrines are obtained in up to 72% ee (Equation (54)). a-Aminonitriles are prepared directly from aldehydes, amines, and cyanotrimethysilane by the BiCl3-catalyzed Strecker-type reaction. 

At present there are four good methods for preparing secondary nitramines. They are the oxidation of nitrosamines by peroxytrifluoro-acetic acid (5), the chloride-ion catalyzed direct nitration of amines (3), the nitrolysis of dialkylamides with nitric acid (16), and the alkaline nitration of amines with acetone cyanohydrin nitrate (6). We have found that treating two equivalents of several secondary aliphatic amines... 

Resolution The reagent 1 reacts with racemic alcohols, thiols, amines, and cyanohydrins to give diastcreomeric derivatives that can be separated by column chromatography or crystallization. Subsequent hydrolysis gives the enantiomers and 1 is recovered. With racemic alcohols, preferential acetalization of the (R)-cnantiomers is observed. 

Oxabicyclo[2.2.1]hept-5-cn-2-one derivatives (ketals, cyanohydrins) were prepared in an optically pure form, hence optically pure -functionalized amines can be prepared via the diastereoselective cycloaddition of organic azides. Such transformations have been described for ethoxycarbonyl azide and /ert-butoxycarbonyl azide54, 5. For example 3-amino-3-deoxy-a-altropyranoside hydrochloride 20 was prepared from the dibenzyl acetal 19ss. 

The cycloaddition of ethoxycarbonyl azide to racemic O-acetyl cyanohydrin 21 was performed either at 40 °C in acetone or at room temperature and without solvent in the presence of a metal salt (zinc(II) acetate, nickel chloride or copper(I) cyanide) as catalyst54. The required dihydro-triazole 22 (isolated from the 2 1 mixture of regioisomers) was directly converted to the jS-acetoxy amine via migration of the endo-acetoxy group. The Ivans relationship of the hydrogen atoms at C-5 and C-6 was deduced from ll NMR. 

Active carbonyl compounds interfere by forming acetals or ketals by reaction with methanol. The interference can be avoided by adding hydrogen cyanide to form cyanohydrins that do not interfere. Other interfering substances include mercaptans and certain amines, which react with iodine, and various oxidizing substances such as peroxy acids, diacyl peroxides, and quinones, which react with iodide to produce iodine. 

Use is made of the facile hydrogenation of nitro groups to prepare a-hydroxy primary amines from nitromethane-ketone addition products (Eqn. 19.22). The addition of a little acetic acid to the reaction medium can sometimes improve the yield. The p-hydroxyamines are more easily prepared in this way than by the hydrogenation of the corresponding cyanohydrin. a-Chloro nitro compounds are selectively hydrogenated to the oxime over palladium under... 

The five-membered homolog of 390 (R = R = H, = 0) gave the dimethylaminomethylene derivative 381 upon treatment with dimethyl-amine. The formyl compounds 390 = 0,1) and the dimethylaminomethylene derivatives 392 were transformed by amines, hydrazines, and hydroxylamine into the corresponding 3-aminomethylene derivatives of type 394. - ° The dimethylaminomethylene compound 381 and the formyl derivative 390 (R = R = H, = 0) afforded cyano derivatives 395 on treatment with acetone cyanohydrin. - Compound 395 (R = NMe2) was hydrolyzed to the acetic acid derivative 396 in concentrated hydrochloric acid. Treatment of the (dimethylaminomethylene) pyrrolo-[2,l-i ]quinazoline 381 with formic acid furnished the bis derivative 397. The formyl and dimethylaminomethylene groups of compounds... 

Addition of acetone cyanohydrin to 606 in the presence of a catalytic amount of triethyl-amine affords cyanohydrin 607 as a mixture of isomers. Ketalization with cyclohexanone dimethyl acetal gives a near statistical mixture (45 55) of (2S, 3 S)-608 and (2R, 3 S)-609, which is separable by column chromatography (96% overall yield). Each isomer, with an optical purity greater than 95%, is a versatile intermediate, and they have been used in the synthesis of amino sugars A-benzoyl-L-acosamine (614) [189] (Scheme 85) and A-benzoyl-L-daunosamine (615) [190]. 

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