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A templated backfolding concept to construct a [2]catenane was attempted via a quasi[1]catenane showing an inverted spiro geometry. The template is covalently connected to the ketal-connected semi-perpendicular-arranged linear precursors and spatially directs the sterically congested backfolding macrocyclizations that are required to give a quasi[1]catenane. So far, we are unable to hydrolyze the cyclic ketal to liberate the [2]catenane.

Enantiopure 8-benzylprotoberberines were synthesized by two consecutive Pictet-Spengler (PS) condensations with protected 3,4-dihydroxyphenylacetaldehydes. The first PS to (+)-(R)-norprotosinomenine was optimized to 90 % ee with 5 mol-% of (R)-TRIP as chiral Bronsted acid (> 99 % ee after trituration). The second PS did not require any catalyst, and its regioselectivity was strongly dependent on the solvent: 99: 1 para selectivity was obtained in trifluoroethanol leading to (+)javaberine A; 81: 19 ortho selectivity was reached in apolar aprotic solvents for the synthesis of (+)-javaberine B. Complete, natural diastereoselectivity was observed in the second PS. Through selective catechol oxidation the spirocyclic alkaloid (-)-latifolian A was prepared from protected (+)-javaberine A.

Item does not contain fulltext An enantioselective synthesis of the right-hand substructure of solanoeclepin A has been developed. The key step was an intramolecular [2+2] photocycloaddition between an allene and a butenolide providing a methylenecyclobutane with three quaternary carbon atoms in a complex tetracyclic framework. Other crucial steps included an enantioselective Noyori transfer hydrogenation of a ketone, a diastereoselective silver-mediated silyl dienolate allylation, and a diastereoselective cyclopropanation of an allylic alcohol. The installation of the bridgehead methyl group by reduction of the lactone moiety proved to be troublesome.

Contains fulltext : 57310.pdf (Publisher’s version ) (Closed access) This paper describes preliminary results in the field of rather unexplored nucleophilic additions to N-phosphoryliminium ions. The synthesis of allylic and non-allylic cyclic amidophosphate-based N,O-acetals and their application in C-C bond formation is detailed. In addition, the influence of a chiral auxiliary on the phosphorus atom has been investigated.

A new method has been developed for the synthesis of 2-​alkylidenequinuclidines based on a silver triflate catalyzed intramol. hydroamination of 4-​(prop-​2-​ynyl)​piperidines. Monosubstituted piperidines reacted less efficiently than cis-​disubstituted piperidines, and the reaction was selective for an alkyne moiety, even in the presence of a vinyl group at the 3-​position. The hydroamination occurred readily with a terminal alkyne, as well as with an internal alkyne bearing an aliph. or arom. group at the terminal carbon atom. Using this silver-​catalyzed cyclization, a short procedure was developed for the relay synthesis of the cinchona alkaloids dihydroquinidine and dihydroquinine.

Racemic total syntheses of four spirocyclic oxindole alkaloids are reported. The general starting material was an N-2-butenylated 2-hydroxytryptamine, which underwent a base-mediated Mannich spirocyclisation with a functionalised aldehyde to generate the C-ring. The second key step was a Pd-catalysed cyclisation of an alpha-keto ester enolate (in the original aldehyde) onto an allylic carbonate (in the N-substituent) to form the D-ring. The stereoselectivities of the key steps were moderate, but the isomers were readily purified, so that the natural products could be conveniently prepared, three of them for the first time.

A new class of Michael acceptors based on α,β-unsaturated amino acids has been prepared and applied in asymmetric ­organocatalysis. With the use of thiourea derivatives of cinchona alkaloid-derived catalysts, efficient addition of thiols to the ­dehydroamino acids occurred with formation of β-thiol functionalized α-amino acids in high yields, moderate diastereoselectivities and ee values up to 95%.

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[13361-64-3] C6H12Si (MW 112.27) InChI = 1S/C6H12Si/c1-5-6-7(2,3)4/h1H,6H2,2-4H3 InChIKey = ULYLMHUHFUQKOE-UHFFFAOYSA-N (propargylation agent; allenylation agent; can give addition reactions on the triple bond) Alternate Name: propargyltrimethylsilane. Physical Data: bp 91–93 °C/760 mmHg; 40 °C/140 mmHg; d 0.753 g mL−1; nD20 1.4140. IR (cm−1, neat): 3320 s, 2120 m (CCH); 1250 s, 845 s, 755 w (SiC). 1H NMR: (CCl4, δ ppm): 0.11 (s, 9H, SiMe3); 1.41 (d, J 2.5 Hz, 2H, CH2); 1.66 (t, J 2.5 Hz, 1H, CH).1-4 Solubility: sol ether, THF, CH2Cl2. Form Supplied in: colorless liquid, commercially available. Analysis of Reagent Purity: IR and NMR. Preparative Methods: the main method of preparation is shown in eq 1.1-3 The title reagent can be obtained by other methods,4 but in poor yields. (1) Purification: by distillation. Handling, Storage, and Precautions: usually stored in a refrigerator. The reagent should be handled in a well-ventilated hood.

Since WWI, an estimated 15% of all soldiers killed in combat are attributed to fratricide, and recent military operations show no decline. A substantial amount concerns fratricide incidents between dismounted soldiers. However, most techniques introduced to prevent fratricide focus on inter-vehicle identification (IFF systems). In this feasibility study, we propose a decision support system that warns a dismounted soldier about to engage when there is a high risk of fratricide. The project has won the 2007 Innovation Game organized by the Dutch Ministry of Defense (MoD). The system will run on a new platform that is currently in development within the Dutch Soldier Modernisation Programme. This platform enables information exchange between soldiers and the Battlefield Management System (BMS), among which up-to-date soldier position information from GPS. Together with terrain information, also available in BMS, these soldier positions are taken into account when deriving an instant risk estimation for fratricide in the current shooting direction. The system is demonstrated using a simulation in which the village of Marnehuizen, built to train Military Operations on Urban Terrain (MOUT), serves as an example. The Dutch army has expressed great interest in the outcome of the study, and is currently investigating possibilities for actual implementation

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Racemic Baylis-Hillman carbonates can be converted in densely functionalized products by reaction with cyano esters in the presence of a catalytic amount of a modified Cinchona alkaloid in high enantioselectivities and fair diastereoselectivities. A rational for the observed stereoselectivity is presented