Highly enantioselective water-compatible organocatalyst for Michael reaction of ketones to nitroolefins

A chiral diamine was found to catalyze enantioselective addition of ketones to nitroolefins in aqueous/saline/organic media. The products were obtained with excellent diastereoselectivities (syn/anti = 99:1) and enantioselectivities up to 99%. The reaction could be facilitated using a mild acid. [reaction: see text]     

An efficient approach to 2-substituted N-tosylpiperdines: asymmetric synthesis of 2-(2-hydroxy substituted)piperidine alkaloids

We have developed an efficient and a general approach to chiral 2-substituted N-tosylpiperidines starting from chiral α-substituted-N-tosylaziridines. Using this approach, we have synthesized (+)-coniine. The synthesis of chiral N-tosyl-2-piperidinylethanol 15 and ent-15, was achieved from l- and d-aspartic acids, respectively in few steps. Piperidine 15 was converted into 2-(2-hydroxysubstituted)piperidines of type 2 in optically active form. By applying this strategy, asymmetric syntheses of halosaline (R,R)-2a, (+)- and (−)-sedamine 2b, (+)- and (−)-allosedamine 2c, (+)- and (−)-sedridine 2d, (+)- and (−)-allosedridine 2e, (+)-tetraponerine T-3 3a, T-4 3c, T-7 3b, and T-8 3d have been achieved in high yields. These stereoisomers can be interconverted via Mitsunobu inversion in excellent yields.     

Enantioselective organocatalytic aldol reaction using small organic molecules

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Enantioselective reactions catalyzed by small organic molecules (asymmetric organocatalysis) are a comparatively new and popular segment in the area of contemporary research in asymmetric synthesis. The great synthetic utility of the aldol reaction for the formation of C–C bonds has geared up for a hard battle for research in this area resulting in a rapid evolution of tremendous highly enantioselective chiral catalysts. This review emphasizes asymmetric direct aldol reactions catalyzed by small enantioenriched organic molecules, particularly those involving enamine catalysis through primary and secondary amines. We have made significant efforts to include several important contributions from different groups in this area.     

Enantioselective diethylzinc addition to aldehydes catalyzed by Ti(IV) complex of unsymmetrical chiral bis(sulfonamide) ligands of trans-cyclohexane 1,2-diamine

Titanium(IV) complexes of bidentate trans-cyclohexane 1,2-diamine-based unsymmetrical chiral bis(sulfonamide) ligands were evaluated as catalysts for the asymmetric addition of diethylzinc to aldehydes. The reaction provided secondary alcohols in quantitative yields and very good enantioselectivity (up to 96% ee).     

Catalytic Enantioselective Decarboxylative Allylations of a Mixture of Allyl Carbonates and Allyl Esters: Total Synthesis of (−)‐ and (+)‐Folicanthine

A highly enantioselective decarboxylative allylation of a mixture of enol carbonates and allyl esters has been achieved. The strategic viability of this methodology has been demonstrated through the total synthesis of cyclotryptamine alkaloids (?)‐ and (+)‐folicanthine ( 1 a ) and the formal total synthesis of (?)‐chimonanthine ( 1 b ), (+)‐calycanthine ( 1 c ), and (?)‐ditryptophenaline ( 1 d ).     

Unified strategy for the synthesis of the "miscellaneous" lycopodium alkaloids: total synthesis of (+/-)-lyconadin A

Total synthesis of the Lycopodium alkaloid lyconadin A was achieved in 18 steps starting from a readily available vinylogous ester and bromopicoline. The key step in the total synthesis is a proximity-driven oxidative C-N bond-forming reaction that yields the lyconadin pentacycle from a tetracyclic precursor. The key tetracycle, which has been prepared for the first time, is a versatile intermediate that may be utilized for the total synthesis of a variety of Lycopodium alkaloids. Critical to the success of this plan was the efficient preparation of a pyridine-annulated cycloheptadiene tricycle that promises to be a general strategy to access a variety of seven-membered ring containing natural products.     

Enantioselective one-pot three-component synthesis of propargylamines

[reaction: see text] A copper(I) complex of i-Pr-pybox-diPh has been found to be an efficient catalyst for an enantioselective one-pot three-component synthesis of propargylamines from aldehydes, amines, and alkynes. The reaction has been applied to a wide variety of aromatic aldehydes with excellent yields (up to 99%) and enantiomeric excesses (up to 99% ee). A transition-state model has been proposed to explain the stereochemical outcome of the reaction.     

Activation of DMSO by Phosphonitrilic Chloride: An Efficient Method for Oxidation of Alcohols

A variety of alcohols have been oxidized under mild conditions by a dimethylsulfoxide (DMSO)–chlorophosphazene complex. Sensitive groups such as silyl and tetrahydropyranyl (THP) ethers are stable under this condition.     

Reaction between cis-diaquabisbiguanideruthenium(III) and hexathiocyanatochromium(III) ions in aqueous media. A mechanistic survey on the formation of a dinuclear bridged complex

The reaction between two complex species [Ru(BigH)₂(H₂O)₂]³⁺ and [Cr(SCN)₆]^3– has been investigated in aqueous medium in the pH range 4.00–6.10, and followed in the 21–40 °C range. Pseudo-first order rate constants were evaluated using the chromium complex in a ten-fold excess. The plot of k _obs versus pH has a bell shaped profile. From this and other evidence it was concluded that only the [Ru(BigH)₂(OH)(H₂O)]²⁺ form of the ruthenium complex is reactive under the experimental conditions, and forms the dinuclear complex [Ru(BigH)₂--(SCN)₂-Cr(NCS)₄]⁰. The rate constant for the dinuclear complex formation at 31 °C is (2.57 ± 0.05) × 10^–3 mol^–1 s^–1. H = 60 ± 2 kJ mol^–1 and S = 116 ± 10 J K^–1 mol^–1.