Direct conversion of N-methoxy-N-methylamides (Weinreb amides) to ketones via a nonclassical Wittig reaction

[reaction: see text] N-Methoxy-N-methylamides (Weinreb amides) are converted efficiently into ketones by reaction with alkylidenetriphenylphosphoranes and in situ hydrolysis of the product.     

A Synthesis of an Ionomycin Calcium Complex

Caught in the middle : The ionomycin calcium complex (see structure; O red, Ca green) was the target of an approach featuring the efficient asymmetric synthesis of an allene by a copper(I)‐mediated anti‐selective S_N2′ reaction, a highly stereoselective gold(III)‐catalyzed cycloisomerization of an α‐hydroxyallene, and a Rh‐catalyzed rearrangement of an α‐diazo‐β‐hydroxyketone.

     

Si-directed regiocontrol in asymmetric Pd-catalyzed allylic alkylations using C1-ammonium enolate nucleophiles

Cooperative catalysis enables the direct enantioselective α-allylation of linear prochiral esters using Si-substituted allyl electrophiles. The Si-substituent directs the regioselectivity of enantioselective bond formation and provides products containing synthetically versatile pentafluorophenyl ester and vinylsilane moieties. Critical to the efficacy of this process was the recognition that the ancillary ligand on palladium could be altered to prevent formation of a deleterious ether by-product, whilst retaining enantioselectivity through the Lewis base catalyst. Flexibility such as this is unique to cooperative catalysis events and provides efficient access to an array of enantioenriched products that are orthogonally functionalized and easily modified.     

Driving matrix liquid crystal displays

Liquid crystal displays had a humble beginning with wrist watches in the seventies. Continued research and development in this multi-disciplinary field have resulted in displays with increased size and complexity. After three decades of growth in performance, LCDs now offer a formidable challenge to the cathode ray tubes (CRT). A major contribution to the growth of LCD technology has come from the developments in addressing techniques used for driving matrix LCDs. There are several approaches like passive matrix addressing, active matrix addressing and plasma addressing to drive a matrix display. Passive matrix LCD has a simple construction and uses the intrinsic non-linear characteristic of the LCD for driving. Departure from conventional line by line addressing of a passive matrix has resulted in improved performance of the display. Orthogonal functions have played a crucial role in the development of passive matrix addressing. Simple orthogonal functions that are useful for driving a matrix LCD are introduced. The basics of driving several rows simultaneously (multi-line addressing) are discussed by drawing analogies from multiplexing in communication. The impact of multi-line addressing techniques on the performance of the passive matrix LCDs in comparison with the conventional technique will be discussed.     

Enantioselective Syntheses of Strychnos and Chelidonium Alkaloids through Regio- and Stereocontrolled Cooperative Catalysis

We describe enantioselective syntheses of strychnos and chelidonium alkaloids. In the first case, indole acetic acid esters were established as excellent partner nucleophiles for enantioselective cooperative isothiourea/Pd catalyzed α-alkylation. This provides products containing indole-bearing stereocenters in high yield and with excellent levels of enantioinduction in a manner that is notably independent of the N-substituent. This led to concise syntheses of (−)-akuammicine and (−)-strychnine. In the second case, the poor performance of ortho-substituted cinnamyl electrophiles in the enantioselective cooperative isothiourea/Ir catalyzed α-alkylation was overcome by appropriate substituent choice, leading to enantioselective syntheses of (+)-chelidonine, (+)-norchelidonine, and (+)-chelamine.     

On the governing equations for the compressing process and its coupling with other processes

As a continuation of a recent linear analysis by Mao et al.(Acta Mech Sin,2010,26:355),in this paper we propose a general theoretical formulation for the compressing process in complex Newtonian fluid flows,which covers gas dynamics,aeroacoustics,nonlinear thermoviscous acoustics,viscous shock layer,etc.,as its special branches.The principle on which our formulation is based is the maximally natural and dynamic Helmholtz decomposition of the Navier-Stokes equation,along with the kinematic Helmholtz decompos...     

Callipeltosides A,B and C: Total Syntheses and Structural Confirmation

Since their isolation almost 20 years ago, the callipeltosides have been of long standing interest to the synthetic community owing to their unique structural features and inherent biological activity. Herein we present our full research effort that has led to the synthesis of these molecules. Key aspects of our final strategy include 1) synthesis of the C1–C9 pyran core ( 5 ) using an AuCl₃‐catalysed cyclisation; 2) formation of C10–C22 vinyl iodide ( 55 ) by sequential bidirectional Stille reactions and 3) diastereoselective union of these advanced fragments by means of an alkenylzinc addition (d.r.=91:9 at C9). The common callipeltoside aglycon ( 4 ) was completed in a further five steps. Following this, all three sugar fragments were appended to provide the entire callipeltoside family. In addition to this, D ‐configured callipeltose B was synthesised and appended to the callipeltoside aglycon. The ¹H NMR spectrum of this molecule was found to be significantly different to the natural isolate, further supporting our assignment of callipeltoside B ( 2 ).     

A Regio‐ and Stereodivergent Synthesis of Homoallylic Amines by a One‐Pot Cooperative‐Catalysis‐Based Allylic Alkylation/Hofmann Rearrangement Strategy

Herein, we report a modular synthetic route to linear and branched homoallylic amines that operates through a sequential one‐pot Lewis base/transition‐metal catalyzed allylic alkylation/Hofmann rearrangement strategy. This protocol is operationally trivial, proceeds from simple and easily prepared substrates and catalysts, and enables all aspects of regio‐ and stereoselectivity to be controlled through a conserved experimental protocol. Overall, the high levels of enantio‐, regio‐, and diastereoselectivity obtained, in concert with the ability to access orthogonally protected or free amines, render this a straightforward and effective approach for the preparation of useful enantioenriched homoallylic amines. We have also demonstrated the utility of the products in the context of pharmaceutical synthesis.     

Traversing Steric Limitations by Cooperative Lewis Base/Palladium Catalysis: An Enantioselective Synthesis of α‐Branched Esters Using 2‐Substituted Allyl Electrophiles

Cooperative catalysis enables the direct enantioselective α‐allylation of linear prochiral esters with 2‐substituted allyl electrophiles. Critical to the successful development of the method was the recognition that metal‐centered reactivity and the source of enantiocontrol are independent. This feature is unique to simultaneous catalysis events and permits logical tuning of the supporting ligands without compromising enantioselectivity.