Cascade metathesis reactions for the synthesis of taxane and isotaxane derivatives

Tricyclic isotaxane and taxane derivatives and have been synthesized by a very efficient cascade ring-closing dienyne metathesis (RCDEYM) reaction, which formed the A and B rings in one operation. When the alkyne is present at C13 (with no neighboring gem-dimethyl group), the RCEDYM reaction leads to 14,15-isotaxanes 16a,b and 18b with the gem-dimethyl group on the A ring. If the alkyne is at the C11 position (and thus flanked by a gem-dimethyl group), RCEDYM reaction only proceeds in the presence of a trisubstituted olefin at C13, which disfavors the competing diene ring-closing metathesis reaction, to give the tricyclic core of Taxol 44

An efficient one-pot four-component synthesis of 1H-pyrazolo[1,2-b] phthalazine-5,10-dione derivatives catalyzed by proline

674-679The present report articulates a potential and green method for the synthesis of pyrazolo[1,2-b]phthalazine-5,10-dione by one-pot four component reaction involving phthalimide (1), hydrazine hydrate (2), aldehyde (3) and malononitrile (4). Proline has been utilized as organo-catalyst in a mixed solvent of ethanol and water in the ratio of 2:1 at 80°C. The reaction reveals excellent reactivity, functional group tolerance, and quite high yields without using any extreme reaction condition like strong acid or metal catalyst. Eighteen compounds have been synthesised by this method including five new compounds

In situ enzymatic screening (ISES) of P,N-ligands for Ni(0)- mediated asymmetric intramolecular allylic amination

An in situ enzymatic screening (ISES) approach to rapid catalyst evaluation recently pointed to Ni(0) as a new candidate transition metal for intramolecular allylic amination. This led to further exploration of chiral bidentate phosphine ligands for such transformations. Herein, a variety of P,N-ligands are examined for this Ni(0)-chemistry, using a model reaction leading into the vinylglycinol scaffold. On the one hand, an N,N-bis(2-diphenylphosphinoethyl)alkylamine (‘PNP’) ligand proved to be the fastest ligand yet seen for this Ni(0)-transformation. On the other, phosphinooxazoline (PHOX) ligands of the Pfaltz–Helmchen– Williams variety gave the highest enantioselectivities (up to 51% ee) among P,N-ligands examined

A mild and versatile synthesis of bis(indolyl)methanes and tris(indolyl)alkanes catalyzed by antimony trichloride

1402-1406Antimony trichloride is found to be a mild and efficient catalyst for electrophilic substitution reaction at 3-position of 3-unsubstituted indole derivatives with a variety of carbonyl compounds in acetonitrile to afford the corresponding bis(indolyl)methanes in excellent yields. ⍺,β -Unsaturated carbonyl compounds give tris(indolyl)alkanes under the same reaction conditions. The versatility of this method has been proved with a wide range of aromatic aldehydes with various stereo-electronic factors. This method shows much better selectivity between aldehydes and ketones as well as greater reactivity towards the electron deficient over the electron rich aromatic aldehydes, which are in contrast to the existing methods

Antimony trichloride: A mild and efficient reagent for chemoselective ring

302-307Antimony trichloride mediates regioselective, stereoselective and chemoselective ring opening of oxiranes under mild laboratory conditions with semiquantative yields. A new route to -acetoxychalcones is also explored

An efficient one pot conversion of alkynes to bis(indolyl) and bis(pyrrolyl)alkanes in aqueous ethanol

122-128Mercury (II) chloride efficiently catalyzes the reaction between indoles /pyrrole and substituted phenyl acetylenes to furnish bis(indolyl)alkane and bis(pyrrolyl)alkane in good to excellent yields under room temperature and moderate reaction time. The reaction is carried out in ethanolic water medium

Impact of structural modification on the photophysical response of benzoquinoline fluorophores

Structural influence on the photophysical behavior of two pairs of molecular systems from the biologically potent benzoquinoline family, namely, dimethyl-3-(4-chlorophenyl)-3,4-dihydrobenzo[f]-quinoline-1,2-dicarboxylate, dimethyl-3-(2,6-dichlorophenyl)-3,4-dihydrobenzo[f]quinoline-1,2-dicarboxylate and their corresponding dehydrogenated analogues has been investigated exploiting experimental as well as computational techniques. The study unveils that dehydrogenation in the heterocyclic rings of the studied quinoline derivatives modifies their photophysics radically. Experimental observations imply that the photophysical behavior of the dihydro analogues is governed by the intramolecular charge transfer (ICT) process. However, the ICT process is restricted significantly by the dehydrogenation of the heterocyclic rings. Computational exertion leads to the proposition that the change in the electronic distribution in these molecular systems on dehydrogenation is the rationale behind the dramatic modification of their photophysics