Studies on the Asymmetric Dihydroxylation of Advanced Bryostatin C-Ring Segments

Abstract

The asymmetric dihydroxylation reaction of early stage and advanced Bryostatin C-ring precursors was evaluated. For homoallylic ethers and alcohols, several AD ligands were investigated including a novel class of quinidine-alkynes.

Key words

asymmetric dihydroxylation - Bryostatin - quinidine-based ligands - double stereoinduction - Cinchona alkynes

References

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1

New address: Christian B. W. Stark, Department of Organic Chemistry, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany.

2

New address: J. Frackenpohl, Bayer CropScience GmbH, Chemistry Frankfurt, G836, Industriepark Höchst, 65926 Frankfurt am Main, Germany.

3

New address: Oliver Gaertzen, Bayer CropScience AG, Alfred Nobel Str. 50, 40789 Monheim, Germany.

17

To determine the ratio of diastereoselectivity for the dihydroxylated lactol of 1 the diol was first transformed into the corresponding acetonide, followed by oxidation to lactone 11 (Equation [3] ).

Equation 3

18

The synthesis of these fragments will be presented in due course.

27

Although complete conversion was noted in these experiments, the yield of isolated product was generally low when structurally complex substrates were converted. Thus far, no degradation products could be isolated, implying the formation of highly water-soluble side-products.