Borane imines

Isocyanides, which have carbene-like divalent carbon atoms, also insert into Si-B bond of 1 in the absence of catalysts to give (boryl)(silyl)iminomethanes, which are isolable after conversion to borane-imine complex (eq 40). ... 

Alkylation and hydrolysis of imines alkylation of aldehydes 10-107 Alkylation and hydrolysis of dithianes 10-108 Alkylation and hydrolysis of oxazines and similar compounds 10-109 Reaction of diazo aldehydes with boranes... 

However, the successful isolation of an iminoborane derivative in the reaction of trichloroacetonitrile with diborane indicated that the stability of imino-boranes is not only a function of the nature of the borane but also of that of the imine 16>. 

This cited reaction illustrates that the C=N double bond of iminoboranes is quite stable. Indeed, the C=N bond in these compounds tends to increase its bond order, forming corresponding nitriles, rather than to undergo further 1,2-additions leading to aminoboranes. This suggestion is confirmed by several reported transformations of iminoboranes to nitrile-borane adducts (Eq. (20)) M). Addition across the C=N double bond of iminoboranes is virtually unknown. This event is also true for related imines (e.g., dichloromethylenealkyl-amines) which yield imine-trihaloborane adducts with trihaloboranes rather than to undergo a 1,2-addition (c.f. Sect. VII). 

Solid adducts between (C43) and (C6H5)2C=NH BF3 is sufficiently stable to withstand vacuum sublimation at 120 °C. Attempted preparation of corresponding BC13 derivatives led only to (diphenyl-methyleneimino)boranes 41). Recently, additional imine-trifluoroborane adducts have been described 44h they are listed in Table 8. 

It is apparent that the B-N bond in imine-borane adducts is not very strong and is influenced by the donor and acceptor properties of the components as well as by steric factors. In the infrared spectra of the adducts the ON stretching bands show only slight shifts as compared with those of the free imino derivatives 23>44). 

Thioesterimide-haloborane adducts (c.f. Sect. VI.2, Eqs. (42-44)) can also be classified as imine-boranes. They are intermediated of low stability in the synthesis of monomeric sulfur substituted iminoboranes 27K... 

Imine-borane bonds which are incorporated into annular systems appear to be considerably more stable. A number of such compounds has been prepared by the reaction of nitriles with (cyclohexenylamino)boranes 7>. 

The boron-11 n.m.r. spectrum of the compound [(CH3)3CCH=N-B(C4H9)2]n exhibits a strong signal at -7,4 ppm and a weak one at -38,8 ppm. At 120 °C the signal intensities reverse thus indicating that the dimer reverts to the monomer with increasing temperature 6>. The chemical shifts of imine-borane derivatives (c.f. Eq. (5)) are observed near +1,0 ppm 7>. 

A listening of iminoboranes and imine-boranes is complied in Tables 3 - 8 the particular arrangement is somewhat arbitrary. In Table 3 all aldiminoboranes... 

The first example of allylation of imines using dialkyl 2-allyl-l, 3-dioxaborolane-4,5-dicarboxylates 110 or fi-allyldiisopinocamphcnyl borane 154 was reported in 1995." After hydrolysis of the reaction product, homoallyl primary amine was obtained in 54-90% yield and up to 73% ee (Scheme 3-52). 

In addition to the predominant allyl and crotyl reagents, a large nnmber of allylic borane 1 and boronate derivatives 2 (Eq. 1) with varions snbstitnents (R -R" ) have been reported. Interested readers can refer to the comprehensive Tabnlar Snrvey at the end of this monograph, which covers the literatnre np to the end of 2005. Several reviews on allylic boron componnds and other allylmetal reagents and their additions to carbonyl compounds and imines have been written prior to this one," " and these sonrces may be consnlted if a more in-depth historical perspective is desired. 

O-linked polymer-bound Af-substituted hydroxylamines are prepared by reduction of resin-bound oximes with borane-pyridine complex in the presence of dichloroacetic acid (Scheme 94). Other reducing systems commonly used for imine or oxime reduction are ineffective, including borane-pyridine in the presence of acetic acid. Subsequently, the A-substituted products are acylated and cleaved from the resin to afford Af-substituted hydroxamic acids 220. ... 

Compounds with a low HOMO and LUMO (Figure 5.5b) tend to be stable to selfreaction but are chemically reactive as Lewis acids and electrophiles. The lower the LUMO, the more reactive. Carbocations, with LUMO near a, are the most powerful acids and electrophiles, followed by boranes and some metal cations. Where the LUMO is the a of an H—X bond, the compound will be a Lowry-Bronsted acid (proton donor). A Lowry-Bronsted acid is a special case of a Lewis acid. Where the LUMO is the cr of a C—X bond, the compound will tend to be subject to nucleophilic substitution. Alkyl halides and other carbon compounds with good leaving groups are examples of this group. Where the LUMO is the n of a C=X bond, the compound will tend to be subject to nucleophilic addition. Carbonyls, imines, and nitriles exemplify this group. 

A Princeton group announced the first synthesis of L-5-deazaFA (91) via a path which to date remains the shortest and most direct route to this series [79, 80], In one step, reaction of 2,4-diamino-6-hydroxypyrimidine (87a) with purified triformylmethane [81a,b] produced 2-amino-5-deazapterin-6-carbox-aldehyde (88a), which was characterized as the acetamide (89a). Reaction of (89a) with dimethyl p-aminobenzoyl-L-glutamate in glacial HOAc afforded an intermediate imine which was reduced in situ with borane-triethylamine, yielding (90). Saponification of the amide and esters then completed the synthesis of (91) in 62% yield from (88a) (Scheme 3.18). Adaptation of this... 

Bis(phosphoranimine) ligands, chromium complexes, 5, 359 Bis(pinacolato)diboranes activated alkene additions, 10, 731—732 for alkyl group functionalization, 10, 110 alkyne additions, 10, 728 allene additions, 10, 730 carbenoid additions, 10, 733 diazoalkane additions, 10, 733 imine additions, 10, 733 methylenecyclopropane additions, 10, 733 Bisporphyrins, in organometallic synthesis, 1, 71 Bis(pyrazol-l-yl)borane acetyl complexes, with iron, 6, 88 Bis(pyrazolyl)borates, in platinum(II) complexes, 8, 503 Bispyrazolyl-methane rhodium complex, preparation, 7, 185 Bis(pyrazolyl)methanes, in platinum(II) complexes, 8, 503 Bis(3-pyrazolyl)nickel complexes, preparation, 8, 80-81 Bis(2-pyridyl)amines... 

A catalytic asymmetric in situ reduction of N-H imines has been achieved in a sequence in which trifluoroacetophenones, ArCOCF3, are first converted to silylimines [using LiN(SiMe3)2], and then on to give trifluoromethylated amine salts, Ar-C(CF3)-NH2.HC1, in good to excellent yield and ee.5s The intermediate N-H imines can be isolated via methanolysis of the N-Si bond, while the enantioselective reduction can be carried out using a chiral borane auxiliary. 

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