Amino boranes

Boracyclohexa-2,5-diene, 1-alkyl-synthesis, 1, 642 Borane, amino-bonds, 1, 630... 

Supported borane amino alcohol complexes and other supported Lewis acids... 

Pis(trimethylsilyl)amino)chloro((trimethylsilyl)amino)borane [10078-93-0]... 

Amine boranes have been examined by a variety of spectroscopic methods (24—29). The boron-substituted alpha-amino acids have been utilized in animal model studies. These compounds along with their precursors and selected derivatives have been shown to possess antineoplastic, antiarthritic, and hypolipidemic activity (30—32). The boron amino acid analogues are also being evaluated for possible utility in boron neutron capture therapy (BNCT) (33). 

The reduction of (aLkylarnino)haloboranes using hydride reagents can provide a convenient route to (aLkylamino)boranes for example, LiAlH has been utilized to prepare bis (dimethyl amino)borane [23884-11-9] from chi orobis (dimethyl amino)borane [6562-41-0] (68). When this same strategy is appHed to (bis(trimethylsi1y1)amino)ch1oro((trimethylsi1y1)amino)borane [10078-93-0] the expected compound is obtained along with the formation of two... 

The most successful of the Lewis acid catalysts are oxazaborolidines prepared from chiral amino alcohols and boranes. These compounds lead to enantioselective reduction of acetophenone by an external reductant, usually diborane. The chiral environment established in the complex leads to facial selectivity. The most widely known example of these reagents is derived from the amino acid proline. Several other examples of this type of reagent have been developed, and these will be discussed more completely in Section 5.2 of part B. 

The hydride-donor class of reductants has not yet been successfully paired with enantioselective catalysts. However, a number of chiral reagents that are used in stoichiometric quantity can effect enantioselective reduction of acetophenone and other prochiral ketones. One class of reagents consists of derivatives of LiAlH4 in which some of die hydrides have been replaced by chiral ligands. Section C of Scheme 2.13 shows some examples where chiral diols or amino alcohols have been introduced. Another type of reagent represented in Scheme 2.13 is chiral trialkylborohydrides. Chiral boranes are quite readily available (see Section 4.9 in Part B) and easily converted to borohydrides. 

The synthesis of cZos o-borane dianions B H (1-7) relies principally on thermolysis reactions of boranes in the presence of either BH4 or amino-borane adducts. " The yields... 

When /V-arenesulfonyl-a-amino acid derived boranes 13 and 14 are used in substoichiometric amounts in order to mediate enantioselective aldol additions of a,a-dimethyl substituted ketcnc acetal 15, /J-hydroxycarboxylic esters 16 are obtained in enantiomeric excess of 84 to > 99 %3fi. 

Ammoniak und prim. Amine spalten Trialkyl-borane nur bei hohen Temp, zu Koh-lenwasserstoffen und Amino-boranen1. Zur Protonolyse von Trialkyl-boranen ist Platin(II)-acetat ebenfalls geeignet2. 

Benzoxazole reagieren mit Diboran in 1,2-Dimethoxy-athan bei 25° unter Amin-Boran-Bildung, nachfolgender Umlagerung und Verseifung der 2,3-Dihydro-(benzo-1,3,2-oxazaborole), mit Salzsaure zu den entsprechenden o-Amino-phenolen2 ... 

AuBerst selektive 1,2-Reduktionsmittel sind Bis-[2-methyl-propyl]-aluminiumhydrid1, Tris-[2-methyl-propyl]-aluminium2, Natrium-bis-[2-methyl-propyl]-dihydrido-aluminat3 und besonders 9-Bora-bicyclo[3.3. ljnonan4 (9-BBN, S. 7). Letzteres ergibt zuerst ein Alkoxy-boran, das zweckmaRig mit 2-Amino-athanol gespalten wird. 

Enamines can also be converted to amino alcohols via hydroboration. Allene-boranes react with aldehydes to give alkyne-alcohols. ... 

Tetrasubstituted phosphinous amides of the type R2NPPh2 have been successfully arylated at phosphorus by the action of bromobenzene, in a process catalyzed by NiBr2, to give the aminophosphonium bromides [R2NPPh3] Br [109]. Other representative members of this class form phosphane-borane complexes [62], are aminated at phosphorus by chloramine to yield bis(amino)phos-phonium salts [110] and have been claimed to be protonated at phosphorus by ethereal tetrafluoroboric acid, as determined by NMR analysis [111]. 

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