An Alkene Zipper Reaction

Aaron over at Carbon Based Curiosities has recently posted about one of my favorite reactions, the alkene zipper reaction catalyzed by 1,3-diaminopropane and potassium hydride. Most of the time this reaction works great, but it is thermodynamic and has some problems when your alkyne is stabilized by conjugation. Anyway, an interesting paper appeared on the JACS ASAP web site last week dealing with the alkene version of a zipper reaction. It is a very nice contribution from Doug Grotjahn and co-workers from San Diego State University. It utilizes a bifunctional ruthenium catalyst to walk an alkene down the chain until it reaches an alcohol. Once an enol is generated it quickly tautomerizes to the ketone form thus providing the thermodynamic sink for the reaction to fall into. The imidazole ligand on the catalyst was crucial for success and may be involved in the isomerization. A very interesting example of this difficult to accomplish process.

Douglas B. Grotjahn, Casey R. Larsen, Jeffery L. Gustafson, Reji Nair, and Abhinandini Sharma: JACS 2007, DOI: 10.1021/ja073457i

ASAP Friday

A couple of ASAP articles from JACS stood out for me this morning.

The first is an interesting Nazarov cyclization followed by a Wagner-Meerwein rearrangement reported by Alison Frontier. Depending on the substitution, the path of the Nazarov is altered and the reaction is terminated by either a hydride shift or an aryl shift. Interesting paper well worth reading the details.

Jie Huang and Alison J. Frontier, JACS DOI: 10.1021/ja0716148

Mukund Sibi reported a novel organocatalytic method for the conjugate addition of hydroxylamines. The catalyst provides for both hydrogen bonding activation of the substrate and hydrogen bond-directivity for the incoming nucleophile.

Mukund P. Sibi and Kennosuke Itoh, JACS DOI: 10.1021/ja071739c

ASAP Thursday

Some good papers have shown up on ASAP this week. Here's two that rose to the top for me.

First is a contribution from Shu Kobayashi with some very interesting chemistry using chiral Calcium complexes. The reaction he investigated was the Michael addition of glycine derivatives with acrylates. He showed the importance of an enolizable proton on the bis-oxazoline ligand and suggests that the reactive species is a calcium Brønsted base. This generates a chiral calcium enolate that undergoes Michael addition to the acceptor. Subsequently, an intramolecular Mannich reaction ensues to afford pyrrolidines in very high selectivity.

Susumu Saito, Tetsu Tsubogo, and Shu Kobayahsi, JACS, DOI: 10.1021/ja0709730

Organocatalysis is all the rage now, and even we are trying our hand at some. Xiao has just reported a slightly new twist on organocatalysis by carrying out an intramolecular Friedel-Crafts reaction with indoles to form tricyclic compounds. Selectivities are are pretty good in some cases.

Chang-Feng Li, Hiu Liu, Jie Liao, Yi-Ju Cao, Xiao-Peng Liu, and Wen-Jing Xiao, OL, DOI: 10.1021/ol0703130

ASAP Thursday

The first thing I do when I get into the lab in the morning is make my coffee. The second thing is to see what has appeared on the web journals. I suppose since I'm blogging that I should share with you the articles that catch my eye. Here's a couple from today.

Karl Scheidt has a very nice example of umpolung chemistry catalyzed by N-heterocyclic carbenes in a [3+3] cycloaddition. This appeared on the web yesterday.

Audrey Chan and Karl A. Scheidt, JACS DOI: 10.1021/ja0709167


Interestingly, I was just teaching my synthesis students about the utility of diazo compounds for cyclopropanation and Wolff rearrangements and what appears on OL this morning? A very nice and practical method for the preparation of diazo compounds. This could come in handy.

Muhammad I. Javed and Matthias Brewer, OL DOI: 10.1021/ol070515w