Boranes, reaction with azides

The utilization of a-amino acids and their derived 6-araino alcohols in asymmetric synthesis has been extensive. A number of procedures have been reported for the reduction of a variety of amino acid derivatives however, the direct reduction of a-am1no acids with borane has proven to be exceptionally convenient for laboratory-scale reactions. These reductions characteristically proceed in high yield with no perceptible racemization. The resulting p-amino alcohols can, in turn, be transformed into oxazolidinones, which have proven to be versatile chiral auxiliaries. Besides the highly diastereoselective aldol addition reactions, enolates of N-acyl oxazolidinones have been used in conjunction with asymmetric alkylations, halogenations, hydroxylations, acylations, and azide transfer processes, all of which proceed with excellent levels of stereoselectivity. 

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. 

Secondary amines are formed by reaction of boranes with alkyl or aryl azides. The most efficient borane reagents are monoalkyldichloroboranes, which are generated by... 

In 2013, Hackenberger and coworkers [66], in Berlin, reported the cycloaddition of a borane-protected alkyne-phosphonite with azides to form borane-protected triazole-phosphonites (Scheme 9.24). In this reaction protocol, we have a sequence of two different couplings with two different azido reagents in the first, we have a CuAAC cycloaddition, followed by a metal-free Staudinger phosphonite reaction. 

The azido group is inert to boronic esters but reacts readily with alkyldichlorobo-ranes [70]. Section 8.4.1 describes the conversion of boronic esters into (alkyldichloro)boranes and their reaction with azides. 

Amines and Azides. A wide variety of organic azides has been converted to alkytetkylaminea by reaction with trlethyl borane followed by methanol-ysis of the intermediate. Enamines may be reduced to the corresponding... 

The synthesis of phosphorous-functionalized click ligands also requires special conditions. Phosphine building blocks need be protected as either the corresponding borane complex (l-2a and 4-5a) or oxide (l-2b and 4—5b) in order to prevent an undesirable Staudinger reaction with the azide synthons (Scheme 1). A range of bi-and tridentate P,N click ligands have been synthesized, and the free clickphines (3 and 6) are liberated by a final deprotection of the phosphine group with either DABCO in the case of the borane complexes [86-90] or reduction with tri-chlorosilane [88-92] in the case of the phosphine oxides. 

Organoboranes react with a mixture of aqueous NH3 and NaOCl to produce primary amines. It is likely that the actual reagent is chloramine NH2CI. Chloramine itself,hydroxylamine-O-sulfonic acid in diglyme, and trimethyl-silyl azide " also give the reaction. Since the boranes can be prepared by the hydroboration of alkenes (15-16), this is an indirect method for the addition of NH3 to a double bond with anti-Markovnikov orientation. Secondary amines can be prepared by the treatment of alkyl- or aryldichloroboranes or dialkylchlorobor-anes with alkyl or aryl azides. 

Secondary amines are formed by reaction of trisubstituted boranes with alkyl or aryl azides. The most efficient borane intermediates to use are monoalkyldichloroboranes, which are generated by reaction of an alkene with BHC12 Kt20.148 The entire sequence of steps and the mechanism of the final stages are summarized by the equations below. 

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