Diborane oximes

Diboran reduziert Oxime meistens bereits bei 20° unter Verbrauch von zwei Hy-drid-Aquivalenten zu den entsprechenden Hydroxylaminen1 ... 

Bcnzophenon-oxim und Dicyclohexylketon-oxim werden in Bis-[2-methoxy-athyl]-ather bei 105-110°, 1,3-Diphenyl-propanon-(2)-exim in 1,4-Dioxan bei 85-90° durch Diboran zu den Hydroxylaminen reduziert . 

O-Alkyl-oxime werden durch Diboran in siedendemTHF7oder langsamer bei 20°7 8 durch zwei Hydrid-Aquivalente in Amin und Alkohol gespalten. 

Addition of sodium hydroxide solution during work-up of a reaction mixture of oxime and diborane in THF is very exothermic, a mild explosion being noted on one occasion. 

Whereas diborane in tetrahydrofuran reduces oximes only at 105-110 , oxime ethers and oxime esters are reduced to amines and alcohols at room temperature in good yields. For example the p-nitrobenzoyl ester of cyclohexanone oxime gave a 67% yield of cyclohexylamine and 81% yield of p-nitrobenzyl alcohol [948]. 

Diborane in THF has been successfully used for reduction of aliphatic and aromatic oximes to hydroxylamines. Reported yields are highly variable although the low... 

The asymmetric reduction of oximes of 2-trifluoroacetyl furan, by using diborane with a chiral amino alcohol, has also allowed synthesis of both enantiomers of trifluoroalanines in an elegant manner. The key step in this synthesis is the separation of the (Z) and ( ) isomers of the oximes (Figure 5.4). ... 

In gleicher cheraischer Ausbeute, jedoch mit einer optischen Ausbeute von 76%, laBt sich Acetophenon-(O-methyl-oxim) mit Lithium-alanat in Gegenwart eines aus Diboran und (S)-2-Amino-3-methyl-l,l-diphenyl-butanol gebildeten Boran-Adduktes zu (S)-l-Amino-1-phenyl-ethan reduzieren2. 

Auch O-Acyl-oxime lassen sich zu den entsprechenden primaren Aminen reduzieren. Da hierbei jedoch nicht nur der Oxim-Teil des Molekiils sondern auch der Acyl-Teil reduziert wird, benotigt die Reduktion z. B. bei Verwendung von Diboran die doppelte Menge an Hydrid wie bei der Reduktion von 0-Alkyl-oximen4. 

Metals. Forms complex hydrides, which may explode in air, with Li and Al.9 Octanal Oxime and Sodium Hydroxide. Very exothermic and sometimes explosive reaction occurs on adding NaOH to a reaction mixture of the oxime and diborane in THF.9... 

Optically active amines. Esterification of an oxime, for example 2-hydroximino-1-phenylpropane (1), with a chiral carboxylic acid chloride, S-( + )-2-phenylbutyric acid chloride (2), gives an oximoester (3), which on reduction with diborane gives a mixture of optically active amines (4a, 4b) in which the S-enantiomcr (4a) predominates slightly. (The optical yield is about 6%.)... 

Since hydroxylamines, as well as their precursor oxime derivatives, are reduced by diborane to amines, the reaction has been extended by reducing the initially formed hydroxylamine intermediates (57) to amines (58). Thus excess borane reduces nitroalkenes (56) to amines (58) in the presence of a catalytic amount of sodium borohydride (equation 32). 

Oximes.—Oximes of some saturated ketones are reduced by aqueous alkaline sodium borohydride under reflux to give the corresponding alcohols. Selective reduction of a 3,17-dioxime is possible, at C(3). a -Oximino-ketones afford diols. Diborane, in contrast, reduces oximes to give alkyl hydroxylamines a recent variant using sodium borohydride on silica gel in benzene gave the... 

Hydroxylamine converts a 16a-bromoandrostan-17-one (216) cleanly into the 17-oxime (217) of the 16a-hydroxy-ketone,""" closely paralleling the action of hydrazine."" Reduction of the oxime-acetate (218) with diborane gave the 17/8-acetamido- 16a -acetoxy-derivative (219)."""... 

Nicotra et al. observed that 144 or 145, obtained by mercury-induced cycli-zation of 142 and 143, could not be converted to the desired iodo compound 146. The workers had to resort to introducing the 2-deoxynitrogen substituent after the phosphonate had been introduced as shown in Scheme 30. The ketone was converted to an oxime and with diborane gave the gluco isomer 149 in 64% diastereomeric excess [41]. 

Carbonyl compounds (after ref. 5]. McMurry58 desired to selectively reduce an olefinic double bond with diborane in the presence of a keto group. This was successfully achieved by conversion to the dinitrophenylhydrazone, hydroboration and removal of the protective group by ozonolysis in ethyl acetate at — 78°. Oximes and oxime acetates are reduced by BH3. Attempted protection by ketalization in this case was unsuccessful because of simultaneous migration of the double bond. 

Reduction of oximes. Aldoximes and ketoximes are reduced by diborane in THF at 25° to the corresponding N-monosubstituted hydroxylamines in very good yield.3 If the reaction is carried out at 105-110°in a diglyme-THF solution, the reduction is carried to the corresponding amine. The reaction probably proceeds by way of the hydroxylamine since hydroxylamines are reduced to amines in high yield under these conditions ... 

A reducing agent that converts all types of oximes equally into iV-mono-substituted hydroxylamines is diborane 92 for example, diborane reduces cyclohexanone oxime to iV-cyclohexylhydroxylamine in 82% yield and similarly affords A-heptyl- (81%), A-(/ -nitrobenzyl-(68 %), and iV(-a>methylbenzyl)-hydroxylamine (55%). 

The nitroketone (465) was converted to the oxime acetate (466) which was treated with diborane to reduce the imine group followed by hydrogen to reduce the nitro group and give the diamine (467). The diamine condensed with triethyl orthoacetate to yield dazepinil (471) Scheme 5.110.) [628]. An improved route began with o-toluidine (468) which was iV-protected to allow the directed metallation of the methyl group. Treatment with the SchifPs base (469) followed by deprotection and exposure to triethyl orthoacetate gave dazepinil in improved yield [629]. This benzodiazepine has antidepressant properties. 

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