Diamines chiral reagent

There is one report of a chiral reagent based on allylaluminum chemistry1 2 3 4 5 10. Bis(2-methyl-propyl)-2-propenylaluminum is treated with tin(II) triflate and chiral diamine ligand 4 to give a reagent, presumably a chiral allyltin species, that reacts with aldehydes at — 78 "C. Good enantioselectivity (80 -84% ee) is obtained with aromatic aldehydes, but with aliphatic aldehydes the selectivity is somewhat lower (53-64%)10. 

Sparteine has been widely studied as a catalyst for asymmetric synthesis. Because only (—)-sparteine 10 is commercially available, there has been much interest in the development of (-l-)-sparteine mimics, among which the most important is diamine 467, which has been employed as a chiral reagent or catalyst in a large number of asymmetric synthesis procedures <2006S2233>. 

A series of chiral diamine auxiliary reagents (106) were synthesized from (S)-proline by Mukaiyama and co-workers (107,108). Reaction of the diamines with LAH gave reducing complexes (eq. [28]), which were then evaluated by reduction of acetophenone under a variety of experimental conditions. A large number... 

Trons-l,2-diaminocyclohexane, the most popular representative of the primary diamines and its derivatives, has been widely utilized in the field of stereoselective organometallic catalysis as chiral reagents, scaffolds, and ligands [137]. This C2 symmetrical chiral diamine first reported in 1926 by Wieland and co-workers [193] is commercially available, since it is a component in a byproduct amine stream generated during the purification of 1,6-hexanediamine that is used in the industrial Nylon 66 production. The racemic mixture of this diamine can be easily... 

These chiral C2 symmetric 1,2-diamines have been used to prepare chiral reagents containing aluminum or boron, which have proved to be highly effective Lewis acid catalysts for several synthetic reactions. 

The highest ee s reported to date for the addition of achiral organometallic reagents in the presence of aprotic chiral additives were observed with the C2-symmetric diamines 10, 11 and 12 (Table 25)13 — 15. Enantioselectivities as high as 89% ee were observed with chiral auxiliary 1012. Addition of phenyllithium to pentanal proceeds with lower enantioselection that the analogous addition of butyllithium to benzaldehydeu. Generally, the enantioselcctivity in-... 

When a mixture of aldehydes and (Z)-l-ethylthio-l-trimethylsilyloxy-l-propene is added slowly to a solution of tin(Il) triflate and 10-20 mol% of the chiral diamine 4 in acetonitrile, /1-silyloxy thioesters 5 are obtained in high simple diastereoselection and induced stereoselectivity. Thus, the chiral auxiliary reagent can be used in substoichiometric amount. A rationale is given by the catalytic cycle shown below, whereby the chiral tin(II) catalyst 6 is liberated once the complex 7 has formed33. 

Addition of organolithiutn reagents in toluene to A-cyclohexyl enimines in the presence of chiral nonracemic diethers or diamines (1.2-2,4 equiv) gives, after hydrolysis, //-substituted aldehydes2. It is important to note that these reactions do not occur in the absence of the chiral additive which can be recovered quantitatively for reuse without loss of enantiomeric purity6. 

Treatment of a chiral amine with phosgene is the cheapest way to prepare symmetrical ureas [29]. Nevertheless, due to the toxicity and reactivity of that reagent, it can advantageously be replaced by triphosgene [30] or l,l -carbonyldiimidazole [31-34] or other derivatives such as l,l -carbonyldi-2(lH)-pyridinone [35]. This procedure can be extended to thiophosgene (Scheme 1) and its thio-analogues, such as l,l -thiocarbonyldi-2(lH)-pyridinone to produce thioureas [36] chiral diamines can thus be transformed into the corresponding monoureas or monothioureas. 

The enantioselectivity of Sn(II) enolate reactions can be controlled by chiral diamine additives. These reagents are particularly effective for silyl thioketene acetals.162 Several diamines derived from proline have been explored and l-methyl-2-(l-piperidinomethyl)pyrrolidine 21 is an example. Even higher enantioselectivity can be achieved by attachment of bicyclic amines to the pyrrolidinomethyl group.163... 

Scheme 7-67. Reagents and conditions Sn(OTf)2, chiral diamine, -Bu2Sn(OAc)2, CH2C12, —23°C (68%, anti/syn = 80/20).

Scheme 7-82. Reagents and conditions a Sn(OTf)2, chiral diamine, -Bu2Sn(OAc)2, CH2CI2, —78°C (95%). b (1) HN3, PI13P, DEAD, benzene, room temperature (82%) (2) PI13P, H2O, THF, 55°C (90% yield based on 82% conversion).

A diastereoselective synthesis of vicinal diamines has been described79. The aldehydes 56 derived from chiral amino acids 55 were converted into the A-benzylimines 57 and the latter were treated with organometallic reagents R2M in the presence of cerium(III)... 

The C2 symmetric chiral diether 28" and the naturally occurring chiral diamine, (—)-sparteine (29), have been the most successful external chiral ligands for asymmetric conjugate addition of organolithium reagents. The rest of this review highlights organolithium addition, which is mediated or sometimes catalyzed by 28 or 29. 

Polymerization of racemic 1-phenylethyl methacrylate (PEMA) using a chiral complex of a Grignard reagent with a diamine as an initiator may proceed by reaction of only one of the two enantiomers to give an optically active polymer. 

One major advantage of chiral auxiliary reagents over chiral a-substituted reagents is the fact that the chiral diol or diamine unit is not modified in the bond-making process and is thus potentially recyclable. The preparation of enan-tiomerically pure a-substituted reagents requires a stereoinductive transformation... 

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