Organic Chemistry I

Selected recent publications -2001

"Enzymatic kinetic resolution of 1-(3'-furyl)-3-buten-1-ol and 2-(2'-furyl)-propan-1-ol", A. Bierstedt, J. Stölting, R. Fröhlich, P. Metz, Tetrahedron: Asymmetry 2001, 12, 3399–3407.

Abstract: The enzymatic kinetic resolution of the racemic alcohols 1-(3'-furyl)-3-buten-1-ol (rac-1) and 2-(2'-furyl)-propan-1-ol (rac-2) was investigated by screening a range of lipases and esterases for enantioselective transacylation, as well as for enantioselective hydrolysis. For both alcohols, lipase catalyzed hydrolysis of the derived racemic acetate gave the best results for accessing the desired (S) enantiomers. In case of the secondary alcohol rac-1, ASL turned out to be the optimum enzyme, whereas PPL was superior in case of the primary alcohol rac-2. Additionally, an alternative access to (S)-2via Oppolzer's camphor sultam methodology is described.

"Total synthesis of pamamycin-607", Y. Wang, H. Bernsmann, M. Gruner, P. Metz, Tetrahedron Lett. 2001, 42, 7801–7804.

Abstract: The macrodiolide antibiotic pamamycin-607 has been synthesized by coupling of the two hydroxy acid constituents using the Yamaguchi method. While the final lactonization with formation of the ester linkage between C(1) and the C(8') oxygen proceeded with complete C(2) epimerization, the alternative ring closure involving the carboxylic acid of the smaller fragment and the hydroxyl group of the larger fragment yielded the target molecule.

Synthesis of Highly Substituted Methylenecyclohexenes Using New Domino Reactions with Sultones, B. Plietker, D. Seng, R. Fröhlich, P. Metz, Eur. J. Org. Chem. 2001, 3669–3676.

Abstract: New methods for the synthetic elaboration of sultones with concomitant desulfurization have been developed. Alkylation of sultones with (iodomethyl)trimethylsilane followed by treatment of the resultant silyl compound with tetrabutylammonium fluoride gave rise to sulfur-free methylenecyclohexenes. In a more straightforward fashion, highly substituted compounds of the latter type were readily accessible by alkylation of α-metallated allylic sultones prepared either by deprotonation, radical cyclization/transmetallation, or conjugate 1,6-addition with (iodomethyl)magnesium chloride in a one-pot transformation. An advanced intermediate for the synthesis of several 1,10-seco-eudesmanolides was rapidly constructed using such a protocol.

"A rapid and general access to 3-arylpiperidines", I. K. Büchner, P. Metz, Tetrahedron Lett. 2001, 42, 5381–5383.

Abstract: A short and efficient synthetic sequence to produce a wide variety of 3-arylpiperidines from three simple building blocks is described. Key step is a palladium catalyzed arylation of cyclopentene.

"A shortcut to the smaller fragment of pamamycin-607", H. Bernsmann, M. Gruner, R. Fröhlich, P. Metz, Tetrahedron Lett. 2001, 42, 5377–5380.

Abstract: Starting from a key intermediate for the synthesis of the larger hydroxy acid constituent of pamamycin-607 (1), an efficient three-step route to the methyl ester of the smaller fragment of 1 involving a Yamaguchi lactonization with concomitant C(2) epimerization was developed. Alternatively, the methyl ester of the smaller hydroxy acid portion of 1 was prepared by direct C(2) epimerization.

"Oxidation of α,ω-Diols using the Dess-Martin Periodinane", J. Roels, P. Metz, Synlett 2001, 789–790.

Abstract: Depending on the length of the carbon tether, α,ω -diols either afford cyclic acetoxy acetals or dialdehydes upon treatment with the Dess-Martin periodinane.

"Enantioselektive Synthese der Ricciocarpine A und B (Enantioselective Synthesis of the Ricciocarpins A and B)", C. Held, R. Fröhlich, P. Metz, Angew. Chem. 2001, 113, 1091–1093; Angew. Chem. Int. Ed. 2001, 40, 1058–1060.

Abstract: The furanosesquiterpene lactone ricciocarpin A isolated from a liverwort displays high molluscicidal activity. By twofold application of the catalytic ring-closing metathesis a fast access to the enantiomerically pure title compounds was achieved, and their absolute configuration determined.

"An Efficient Synthesis of the Potent Phytoestrogens 8-Prenylnaringenin and 6-(1,1-Dimethylallyl)naringenin by Europium(III)-Catalyzed Claisen Rearrangement", S. Gester, P. Metz, O. Zierau, G. Vollmer, Tetrahedron 2001, 57, 1015–1018.

Abstract: Starting from commercially available naringenin (3), the flavanoids 8-prenylnaringenin (1) and 6-(1,1-dimethylallyl)naringenin (2) have been prepared in racemic form using prenyl ether 5 as a general intermediate. While a domino Claisen-Cope rearrangement of 5 was the key step in the synthesis of 1, the cytotoxic compound 2 was additionally secured via a europium(III)-catalyzed Claisen rearrangement of 5 at low temperature. Both 1 and 2 display strong estrogenic activities.