Naturalproductman’s Blog

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Archive for May, 2014

[5+2] with rhodium

Posted by naturalproductman on May 14, 2014

Paul Wender and co-workers have reported in Organic Letters on a rhodium catalyzed [5+2] reaction.

propargyl

OL paper

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Posted in Cascade Reactions, Methodology, Rhodium, Transition Metal | Leave a Comment »

Old reagent, new trick

Posted by naturalproductman on May 14, 2014

Ekaterina Budynina and co-workers from Moscow State University have used a Corey ylide to react with alpha,beta-unsaturated ketons to form dihydrofurans.

 
Corey ylide

OL paper

 

Posted in Cascade Reactions, Corey ylide, Methodology, Named Reagents | Leave a Comment »

Macrolactonization towards neopeltolide

Posted by naturalproductman on May 13, 2014

Mingji Dai and co-workers from Purdue have reported in ACIE on alkoxycarbonylative macrocyclization.

Pd

ACIE paper

Posted in Macrolides, Methodology, Palladium, Transition Metal | Leave a Comment »

Dictazole synthesis

Posted by naturalproductman on May 13, 2014

Grey Erwan Poupon and co-workers at CNRS have reported in ACIE on the synthesis of dictazole.

dictazole

ACIE paper

Posted in Alkaloids, Methodology, Total Synthesis, [2+2] | Leave a Comment »

Alcohol to carboxylic acid by an enzyme

Posted by naturalproductman on May 7, 2014

Marco Fraaije and co-workers from the University of Groningen in the Netherlands have reported in ACIE on an enzyme catalyzed oxidation of an alcohol to carboxylic acid.

aldehyde

They did a mechanistic study, which caught my attention. They wanted to test if the carboxylic acid arises from the gem-diol of the aldehyde intermediate or directly from the aldehyde. The experiment was run under 18O-labeled water with 4-nitrobenzaldehyde. They state that if the reaction is spontaneous then the aldehyde will directly give the carboxylic acid with no 18O incorporated in the product, but if it is from the gem-diol, you will have 18O-atoms.

I have a problem with this part because the reaction can still come from the aldehyde if the carboxylic acid had an 18O-atom. The way this would occur is that the aldehyde can get hydrated to the gem-diol then it would be in equilibrium with the aldehyde and give back the aldehyde but this time it has an 18O-atom (STEP 2 product of below). This aldehyde, if oxidized by the enzyme, would yield the carboxylic acid with 18O-atom.

GIF RED
Anyway, interesting paper.
ACIE paper

Posted in Enzymatic, Mechanistic, Methodology | Leave a Comment »

Epoxide cascade ring opening sequence for cyclopropanes

Posted by naturalproductman on May 6, 2014

Marcs Sa and colleague at have reported in JOC on a method to form cyclopropanecarboxamides from a cascade epoxide ring opening sequence.

cyclopropane

JOC paper

Posted in Cascade Reactions, Methodology | Leave a Comment »

Stellatolides

Posted by naturalproductman on May 6, 2014

Carmen Cuevas and co-workers from PharmaMar in Spain have reported in JACS on the isolation and syntheses of stellatolides.

stellatolides

JACS paper

Posted in Cancer, Depsipeptides, Peptides, Total Synthesis | Leave a Comment »

C-H activation within the ruthenium complex

Posted by naturalproductman on May 6, 2014

Another Houk collaboration – this time with Grubbs’ lab. They studied the mechanism of the carboxylate assisted C-H activation of the metathesis catalyst. The SDD basis set was used to approximate the orbitals of ruthenium in this report.

C-H

JACS paper

Posted in C-H activation, Computational, DFT, Methodology | Leave a Comment »

Copper catalyzed [3+2] mechanism

Posted by naturalproductman on May 6, 2014

When I saw the graphical abstract of this paper, the first thing that came to mind was Michael Kerr at the University of Western Ontario, but this paper was from Yong Tang’s group in SIOC in collaboration with Kendall Houk’s computational group to study the mechanism of this [3+2] reaction. They used the LANL2DZ basis set in this paper. Great to hear.

copper

JACS paper

Posted in Cascade Reactions, Computational, Copper, DFT, Methodology, Transition Metal | Leave a Comment »

Polyene cyclization with titanocene

Posted by naturalproductman on May 6, 2014

Juan Cuerva and co-workers from the University of Granada in Spain have reported in JACS on a titanocene mediated polyolefin cyclization reaction that studied with Gaussian calculations. The basis set used to approximate the titanocene catalyst was 6-31G*. From my little knowledge of Gaussian, when using QM calculations to study a reaction mechanism, you need two things: 1) the basis set and 2) the method. The basis set is the linear combination of a set of functions used to approximate the molecular orbitals. There are many kinds of basis sets that can be used for Gaussian. In my experience with transition metals however, I was unable to use the 6-31G* basis set because the transition metals have more complicated molecular orbitals since they have d-orbitals. I had to use the Los Alamos basis set: LANL2Dz. I eventually gave up on my time with Gaussian because I just kept running into problems and eventually had to focus my efforts into experimental work. But hopefully one day I can go back to this stuff again. Afterall, it helps us understand the reaction mechanisms better.

titanocene

JACS paper

Posted in Cascade Reactions, Computational, DFT, Methodology, Titanium, Transition Metal | Leave a Comment »