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Synlett 2004(10): 1811-1813  
DOI: 10.1055/s-2004-829564
LETTER
© Georg Thieme Verlag Stuttgart · New York

Total Synthesis of (+)-Preussin: Control of the Stereogenic Centers by Enantioselective Allyltitanations

Sophie Canova, Véronique Bellosta, Janine Cossy*
Laboratoire de Chimie Organique, associé au CNRS, ESPCI, 10 rue Vauquelin, 75231 Paris Cedex 05, France
Fax: +33(1)40794660; e-Mail: janine.cossy@espci.fr;
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Publikationsverlauf

Received 26 March 2004
Publikationsdatum:
15. Juli 2004 (online)

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Abstract

(+)-Preussin was synthesized in ten steps with an overall yield of 6.4% from phenylacetaldehyde. The three stereogenic centers were controlled by enantioselective allyltitanations of aldehydes.

Key words

preussin - allyltitanation - cross-metathesis

6

Complex (R,R)-Ia (R = MOM) was formed in situ after deprotonation of 3-methoxymethoxypropene by s-BuLi and transmetallation with the correponding chlorocyclo-pentadienyldialkoxytitanium(IV) complex.

7

The enantiomeric excess of (+)-3 was determined by 1H NMR after its derivatization with (S)- and (R)-methoxy-phenylacetic acid.

8

Secondary alcohol 4′ was isolated as a mixture of two diastereomers in a 75:25 ratio. After debenzylation (H2,
Pd/C, quantitative yield), the resulting 1,3-diols were transformed to the corresponding acetonides (dimethoxypropane, PPTS, 90%). According to the 1H NMR and 13C NMR data, the major product has the anti-anti structure (Figure [3] ):

Figure 3

9

Decomposition of the starting material or non-reactivity were observed when other boranes were used [9-BBN, (Cy)2BH].

11

The formation of tetrahydrofuran B as secondary product could be observed during the cyclization process (Figure [4] ).

Figure 4