Synthesis 2014; 46(19): 2663-2671
DOI: 10.1055/s-0034-1378282
paper
© Georg Thieme Verlag Stuttgart · New York

[2+2] Photocycloaddition Studies on Complex Tetronic Acid Esters Related to the Synthesis of Cembranoid Diterpenes

Roland Weixler
Lehrstuhl für Organische Chemie I, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany   Fax: +49(89)28913315   eMail: thorsten.bach@ch.tum.de
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Thorsten Bach*
Lehrstuhl für Organische Chemie I, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany   Fax: +49(89)28913315   eMail: thorsten.bach@ch.tum.de
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Publikationsverlauf

Received: 25. April 2014

Accepted: 12. Mai 2014

Publikationsdatum:
24. Juni 2014 (online)


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Abstract

Twelve different tetronic acid esters bearing two potentially reactive olefinic groups were prepared and subjected to [2+2] photocycloaddition reactions by irradiation at λ = 254 nm in tert-butanol (5 mM). The diastereoselectivity and regioselectivity of the reaction was studied with regard to the synthesis of cembranoid diterpenes. When the tetronic acid core carried an alk-3-enyl substituent in the γ-position and an alk-3-enyloxy substituent in the β-position, the undesired γ-products prevailed and were formed in 48–81% yield. Altering the γ-alk-3-enyl substituent into an alk-3-ynyl or alk-2-ynyl substituent, resulted in formation of the desired β-photocycloaddition products. The latter products were obtained in yields of 56–88%, with two out of three products exhibiting very high regio- and diastereoselectivity.

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