Amino alcohols structure

The N-acetyl derivative of 4-oxazolin-2-one (395) has been shown to function as a Diels-Alder dienophile (77TL3115, 77LA2027). Reaction of (395) with 2,3-dimethyl-l,3-butadiene took place at 160 °C to furnish the cycloadduct (396) in 97% yield. On heating with methanolic potassium hydroxide, the adduct was converted to the c/s-/3-amino alcohol (397) in high yield (Scheme 87). This oxazolinone thus provides a new entry to the /3-amino alcohol structural unit found in many natural substances. 

Oxidation has been reported to occur with a number of compounds which contain nitrogen but possess no a-amino-alcohol structure.11 13 14 Thus, cystine, methionine, and tryptophan are oxidized, though without... 

Natural products having chiral tertiary amine functions were tested among the first catalysts in asymmetric MBH reactions [24, 60]. The importance of the proton donor capacity of the catalyst in the rate and selectivity of the MBH reaction was recognized very quickly, and attention was turned to genuine a-amino alcohol structures, such as the compounds listed in Scheme 5.8 [61]. Results were modest, however. Apart from the earlier discussed (R)-3-HDQ, which catalyzed the MBH reaction at atmospheric pressure (though with no enantioselectivity),... 

It has been concluded from an estimate of Ki and K2 that the uncharged amino alcohol as well as the dipolar structure are present in small concentrations (24). The decomposition is strongly retarded as the pH is lowered and this phenomenon has been explained by assuming the zwitterions to be the active intermediates [Eq. (10)]. 

The stereochemical course of reduction of imonium salts by Grignard reagents was found to depend on the structure of the reagent 714). Hydro-boration of enamines and oxidation with hydrogen peroxide led to amino-alcohols (7/5). While aluminum hydrogen dichloride reacted with enamines to yield mostly saturated amines and some olefins on hydrolysis, aluminum hydride gave predominantly the unsaturated products 716). 

In the case of the bases derived from quaternary heterocyclic ammonium salts, the carbinolamines (5) can react as cyclic aldehyde-ammonias with many reagents with which the amino-aldehyde (7) could react. However, reactions of the carbinolamines which are not characteristic of amino-aldehydes are also known. Carbinolamines can easily be reconverted into the quaternary salts by the action of dilute acids, and they form alkyl ethers very easily with alcohols. If these last reactions do not occur, then this is convincing evidence for the base possessing the amino-aldehyde structure. However, if these reactions do occur this does not provide unambiguous confirmation of the carbinolamine structure. They are also given by the bi-molecular ethers (8), and, in the case of a tautomeric equilibrium... 

Another chiral auxiliary used in diastereoselective addition reactions is the 1,3-oxazine derivative 4a which shows a close structural resemblance to the 1,3-oxathiane 16 (vide supra). However, in contrast to the oxathiane, 4a cannot be readily acylatcd in the 2-position. Therefore, the benzoyl derivative 4b was prepared by condensing amino alcohol 3 with phenylglyoxal. 

To obtain information about the structural requirements of a ligand capable of catalyzing the addition of dialkylzincs to aldehydes, various simple amines, alcohols and amino acid derived amino alcohols were tested as chiral catalysts (Table 27). 

The enantioselective mechanism proposed in the literature stated that the structure I might be the most predominant structure and structure II might be a minor structure. Structure I resulted in (S)-amino alcohol when (S)-amine additive was used. On the other hand, structure II resulted in (R)-amino alcohol when (S)-amine additive was used. When the alkyl group of keto alcohol is methyl, conformation of reactant might he composed mainly of structure I, therefore resulting in highly optically active alaninol as indicated in Scheme 2. However, according to the experimental results, structure I can be a major conformation in this reaction. 

Catalytic amounts of chiral amino alcohols both catalyze the reactions of alkylzinc reagents with aldehydes and induce a high degree of enantioselec-tivity. Two examples are given below. Formulate a mechanism for this catalysis. Suggest transition structures consistent with the observed enantioselectivity. 

As it was shown in [15-18], such compounds, with bridging atoms of deprotonated amino alcohol, are formed when aminoalcoholate complexes of metal (III) react with bivalent 3d-metal ions. Many representatives of these compounds were synthesized in crystalline state the polynuclear compounds were also found to form in aqueous and methanol solutions. The structure of 2Co(III) - Ni(II) tri-nuclear complex, according to [17,18], is shown below in Figure 2. 

The sulfamate ester variant of this chemistry has already been shown to be a very powerful protocol for the syntheses of 1,3-amino alcohols and related /3-amino acids (Equation (90)), as well as iminium ion equivalents (Equation (91)). The further showcases of this chemistry are the total syntheses of the bromopyrrole alkaloids, manzacidins A and C (Scheme 13).234 The cyclic sulfamidate 129 was obtained diastereospecifically from sulfamate 128 using intramolecular rhodium-catalyzed G-H insertion. It was then found to react with sodium azide in NfN-dimethylformamide at room temperature after introduction of the Boc-activating group to afford the 1,3-diamino precursor 130 in 78% yield over 3 steps. Four subsequent manipulations afford the target structure 131. 

The PHOX ligands have a modular structure (Scheme 29.1). They are synthesized from chiral amino alcohols and benzonitrile or bromobenzonitrile the... 

Since the discovery of amino alcohol induced dialkylzinc addition to aldehydes, many new ligands have been developed. It has recently been reported that chiral amino thiols and amino disulfides can form complexes or structurally strained derivatives with diethylzinc more favorably than chiral amino alcohols and thus enhance the asymmetric induction. Table 2 15 is a brief summary of such chiral catalysts. 

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