Stereoselective synthesis of a tetrahydropyranyl diarylheptanoid, ent-diospongin A

The stereoselective synthesis of the unnatural enantiomer of a cyclic diarylheptanoid, diospongin A is described. The salient feature of this synthesis is the formation of a tetrahydropyran ring via the AgOTf-catalysed intramolecular oxa-Michael addition of a β-hydroxy ynone followed by hydrogenation

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(S)-6-(tert-Butyldiphenylsilyloxy)-5-hydroxy-1-phenylhex-1-yn-3-oneC28H30O3Si[α]D28=−4.6 (c 1.0, CHCl3)Source of chirality: l-malic acidAbsolute configuration: (S)

(S)-2-(tert-Butyldiphenylsilyloxy)-6-phenyl-2H-pyran-4(3H)-oneC28H30O3Si[α]D28=+36.3 (c 1.0, CHCl3)Source of chirality: l-malic acidAbsolute configuration: (S)

(2S,4R,6R)-2-((tert-Butyldiphenylsilyloxy)methyl)-6 phenyltetrahydro-2H-pyran-4-olC28H34O3Si[α]D28=+31.4 (c 1.0, CHCl3)Source of chirality: l-malic acidAbsolute configuration: (2S,4R,6R)

(2S,6R)-2-((tert-Butyldiphenylsilyloxy)methyl)-6-phenyldihydro-2H-pyran-4(3H)-oneC28H32O3Si[α]D28=+41.5 (c 1.0, CHCl3)Source of chirality: l-malic acidAbsolute configuration: (2S,6R)

(2S,4R,6R)-2-((tert-Butyldiphenylsilyloxy)methyl)-6-phenyltetrahydro-2H-pyran-4-yl- 4-nitrobenzoateC35H37NO6Si[α]D28=-15.7 (c 1.0, CHCl3)Source of chirality: l-malic acidAbsolute configuration: (2S,4R,6R)

(2S,4R,6R)-2-(Hydroxymethyl)-6-phenyltetrahydro-2H-pyran-4-yl-4-nitrobenzoateC19H18NO6[α]D28=-34.0 (c 1.0, CHCl3)Source of chirality: l-malic acidAbsolute configuration: (2S,4R,6R)