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Organic Synthesis workbook li - Bittner C.

Bittner C. Organic Synthesis workbook li - John Wiley & Sons, 2001. - 292 p.
ISBN: 3-527-30415-0
Download (direct link): bittnerorganicsynthesisworkbook2001.pdf
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Mechanistically, the reaction is explained as an ene-type reaction involving a concerted electron shift (see 28) forming an allylic hydroperoxide and direct hydride reduction of 29 gives rise to the diallylic alcohol 11.
Discussion
12
1 (+)-Asteriscanolide
102
1. Dess-Martin periodinane,
CH2CI2, r. t 0.5 h
2. 21 bar H2, 10 % Pd/C,
EtOH, r.t., 1 h
-^ 12
67 % (over two steps)
Hints The Dess-Martin periodinane is an oxidating reagent.
All olefinic double bonds are reduced in the second step.
Solution
Problem
Discussion The Dess-Martin periodinane 30 (1,1, 1-triacetoxy-1,1-dihydro-1,2-
benziodoxol-3(7H)-one) was originally described in 1983 and has become a widespread reagent for the oxidation of complex, sensitive and multifunctional alcohols.15 The periodinane is a hypervalent iodine species and a number of related compounds also serve as oxidizing agents.
1
(+)-Asteriscanolide
13
A regioselective oxidation takes place.
The cyclic ether is oxidized to a lactone.
1. RuCl3, NaI04, MeCN/CCl4/H20, r. t 5 h, 63 %
The reactive species in this last step for the synthesis of (+)-asteriscanolide is Ru04 prepared in situ from RuCl3 and NaI04. Other common co-oxidants are for example sodium bromate, peracetic acid, oxygen or potassium permanganate. Ru04 is a strong oxidant, however, conditions for ruthenium mediated reactions are very mild (usually a few hours at room temperature) and often only catalytic amounts are sufficient. Water is important for the reaction; thus many ruthenium mediated reactions have been performed in the CC14-H20 solvent system. The addition of MeCN improves yields and reaction times. The configuration of stereocenters close to the reaction site normally remains unaffected. The most common synthetic use of ruthenium is the reaction with alcohols. Cyclic ethers as in this case, are oxidized, yielding lactones, but also a lot of other functional groups are converted: Ru04 usually reacts with unsaturated systems, cleaving the C-C bonds; alkylamines are oxidized to mixtures of nitriles and amides, cyclic amines to lactams and amides to imides. The perruthenate ion RuC)4 for example in TPAP (see Chapter 10) is also useful for the oxidation of several functional groups especially primary alcohols.
1.4 Conclusion
The preceding synthesis realized by Paquette provides (+)-asteriscanolide in 13 steps starting from protected 2-bromo-4,4-dimethylcyclopentenone (2) in an overall yield of 4 %. The key steps are the convergent merging of the readily available enantiopure cyclopentanone sulfoxide 3 and the methyl 4-hydroxybutynoate 14 This domino Michael-Michael addition with a heteronucleophile has
Problem
Hints
Solution
Discussion
1 (+)-Asteriscanolide
not been previously described. The use of the Stille coupling protocol followed by a few more steps furnishes the substrate for a ring-closing metathesis demonstrating that a conjugated diene typified by 10 can be produced by RCM with exceptional efficiency.
1.5 References
1 A. San Feliciano, A. F. Barrero, M. Medarde, J. M. Miguel del Corral, A. Aramburu, A. Perales, J. Fayos, Tetrahedron Lett. 1985, 26, 2369-2372.
2 P. A. Wenders, N. C. Ihle, C. R. D. Correia, J. Am. Chem. Soc. 1988, 110, 5904-5906.
3 . I. Booker-Milburn, J. K. Cowell, L. J. Harris, Tetrahedron.
1997, 53, 12319-12338.
4 L. A. Paquette, J. , M. P. Arrington, A. H. Sadoun, J. Am. Chem. Soc. 2000, 122, 2742-2748.
5 G. H. Posner, J. P. Mallamo, M. Hulce, L. L. Frye, J. Am. Chem. Soc. 1982,104, 4180-4185.
6 L. F. Tietze, Chem. Rev. 1996, 96, 115-136.
7 K. Ritter, Synthesis, 1993, 735-762.
8 J. Stille, Angew. Chem. 1986, 98, 504-519; Angew. Chem. Int. Ed. Engl. 1986, 25, 508-524.
9 E. Piers, R. W. Friesen, B. A. Keay, Tetrahedron 1991, 47, 4555-4570.
10 . H. Lipschutz, S. Sengupta, Org. React. 1992, 41, 135.
11 R. H. Grubbs, S. J. Miller, G. Fu, Acc. Chem. Res. 1995, 28, 446-452.
12 P. Schwab, R. H. Grubbs, J. W. Ziller, J. Am. Chem Soc. 1996, 118, 100-110.
13 S. K. Amstrong, J. Chem Soc., Perkin Trans. 1 1998, 371-388.
14 N. M. Hasty, D. R. Kearns, J. Am. Chem. Soc. 1973, 95, 3380-3381.
15 a) D. B. Dess, J. C. Martin, J. Org. Chem. 1983, 48, 4155-4156; b) D. B. Dess, J. C. Martin, J. Am. Chem. Soc. 1991, 113, 7277-7287.
Organic Synthesis Workbook II
C. Bittner, A. S. Busemann, U. Griesbach, F. Haunert, W.-R. Krahnert, A. Modi, J. Olschimke, P. L. Steck
Copyright 2001 Wiley-VCH Verlag GmbH ISBNs: 3-527-30415-0 (Softcover); 3-527-60013-2 (Electronic)
2
(-)-Bafilomycin Ax (Roush 1999)
2.1 Introduction
(-)-Bafilomycin Ai was first isolated in 1983 by Werner and Hagenmaier from a culture of Streptomyces griseus sp. Sulphuru.' Bafilomycin belongs to a family of macrolide antibiotics. It was found to exhibit activity against Gram-positive bacterial and fungi;2 it also showed immunosuppressive activity and proved to be the first specific potent inhibitor of vacuolar H+-ATPase.3 Structurally, bafilomycin Ai is constructed from a 16-membered tetraenic lactone ring and a /3-hydroxyl-hemiacetal side chain. The intramolecular hemiacetal ring and the macrolactone are linked by a spacer and a hydrogen-bonding system.
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