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Articles Archive for May 2006

Retrosynthetic »

[31 May 2006 | 11 Comments | 16,679 views]

Laszlo Kurti, Barbara Czako; ISBN: 0124297854
A top book published a few years back, this has only just been brought to my attention. Containing the usual list of named reactions, Kurti and Czako have taken a rather similar approach to Warren et al. in their Organic Chemistry, using colour in their detailed mechanisms to ensure clarity. The dicussion of each reaction is also referenced heavily, detailing the primary papers, and subsequent modifications/clarifications. Lastly, and of particular note, the use of each reaction is considered, and examples in seminal total syntheses is …

Still In The RBF »

[31 May 2006 | 13 Comments | 11,087 views]

Fukuyama, Okano and Tokuyama. JACS, 2006, 128(22), 7136. DOI: 10.1021/ja0619455
Continuing somewhat with a heterocyclic theme, Fukuyama has published a short (20 steps), flexable and rather sweet (13% yield) synthesis of yakatemycin. Especially interesting is his use of a ring contraction to put in the cyclopropane; being a spirocyclopropane, this is a reactive beast, so his strategy is rather nice:

Completed as the final step in the synthesis, one can imagine several fingers were crossed during the reaction! This paper also includes the use of an azide displacement / …

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[25 May 2006 | 3 Comments | 4,576 views]

Fürstner, Domostoj, Scheiper. JACS, 2006, ASAP. DOI: 10.1021/ja0617800
Feeling a little rusty with your heterocyclic chemistry? The Fürstner group at the MPI Muelheim seem to know theirs pretty good, with totaly syntheses of Dictyodendrins B, C and E. Differing only by the oxidation levels and the substituents on the C-2 carbon (a ketone sidechain in Dictyodendrin B), their approach allows access to all three.
Their work contains several remarkable transformations, starting with the low-valent Ti convertion of ketoamides to indole derivatives:

Also worth of note is their …

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[21 May 2006 | 5 Comments | 4,448 views]

Kishi, Matsuura, Peters, Anada, Harried, Hao, and Yoshito . JACS, 2006, ASAP. DOI: 10.1021/ja0618954
Kishi and co-workers have just completed their syntheses of the Pteriatoxins A-C, related to their prior work on Pinnatoxin A. Using two of the precursors developed for the latter work, they were able to create the straight-chain analogue, with the necessary addition of a third precursor. They then used a exo-selective DA to assemble the cyclohexene ring, completing the macrocycle.

The DA work in this paper is incredibly interesting …

Fresh Meat »

[16 May 2006 | 2 Comments | 4,091 views]

Yue, Gan, Fan, Yang, Wu, Lin, Ding, and Yue. Org. Let., 2006, ASAP. DOI: 10.1021/ol060551f
Two new targets from the roots of Flueggea Virosa Roxb. ex Willd (Euphorbiaceae), a traditional Chinese medicine source. Clearly dimeric in origin, this beast will take some ingenious work!

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[15 May 2006 | 20 Comments | 6,610 views]

Sorensen and Shipe. JACS, 2006, ASAP, DOI: 10.1021/ja060847g
Furthering their interest in the synthesis of the Guanacastepenes, Sorensen et al have completed the synthesis of members A and D using an interesting fragmentation strategy. However, before this late-stage event, the A and C rings were constructed and united using a Stille cross-coupling. The required cyclobutane was then implaced via a photo-[2+2] cycloaddition:

With this in place, the cyclobutane was fragmented selectively to provide the seven-member ring, trapping with PhSeBr to facilitate elimination in the next step. …

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[10 May 2006 | Comments Off | 3,846 views]

Nicolaou, Bulger and Brenzovich OBC, 2006, Advance Articles. DOIs: 10.1039/b602020h, 10.1039/b602021f
In our second discussion of Nicolaou’s attempted syntheses of amphidinolide N and caribenolide I, we’ll look at their revised strategy for the contruction of these two interesting polyketides. Leaving-off from the last post, their attempt at enyne RCM failed, as did cross-metathesis and palladium mediated coupling. So, in an old-school move, they moved to a Horner-Wadsworth-Emmons olefination to create the enone, which, when methylenated, delivered the troublesome 1,3-diene required.

They then completed a model study to consider methods for selective epoxidation …

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[10 May 2006 | 7 Comments | 5,073 views]

Nicolaou, Bulger and Brenzovich OBC, 2006, Advance Articles. DOIs: 10.1039/b602020h, 10.1039/b602021f
Two papers in OBC this week from the Nicolaou labs, concerning the synthesis of the related structures iso-epoxy-amphidinolide N and des-epoxy-caribenolide I. In another two part discussion, we’ll consider their initial strategy, and a further, more successful attempt.
Their initial synthesis relied upon a late-stage epoxidation, as the allylic epoxide was deemed too sensitive to survive even a standard deprotection. Thus, taking that back to the exocyclic alkene, they were left with a possible enyne metathesis – either ring-closing or in …

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[6 May 2006 | 2 Comments | 5,932 views]

Narasaka, Chiba and Kitamura. JACS, 2006, ASAP, DOI: 10.1021/ja060408h
Tot. Syn. loves oxidative radical cyclisations, so Narasaka’s synthesis of Sodarin was a welcome read this week. Also containing a ß(1,2-cis)-selective glycosidation and a Tsuji-Trost allylation to construct the bicyclic system, this is a particularly ambitious route. First to the radical chemistry:

Using diethylzinc and diiodomethane to generate the cyclopropane, exposure to catalytic quantities of silver nitrate opened the cyclopropane homolytically, oxidising the hydroxyl and leaving a beta radical. This then closed onto the terminal olefin in a 5-exo-trig manner …

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[4 May 2006 | 8 Comments | 5,041 views]

Shibasaki, Fukuta, Mita, Fukuda, Kanai. JACS, 2006, ASAP, DOI: 10.1021/ja061696k
Part-two of our flu-busting master class brings us to Shibasaki’s synthesis of Tamiflu, published, as I mentioned in the previous post, on the same day as Corey’s. This nitrogen-tastic route employs an enantioselective ring-opening of meso-aziridines with azide (hmm… don’t fancy doing that on scale…!), leading to anti-addition of nitrogen.

Using this impressive methodology, they construct the first intermediate in the scheme below, and convert to a meso diamide in …