A simple entry into 1,3-diols from (R)-2,3-cyclohexylideneglyceraldehyde: synthesis of (−)-galantinic acid

Aldehydes 5, 7, and 9 derived from easily accessible (R)-2,3-cyclohexylideneglyceraldehyde 1 were used as novel substrates to obtain both syn- and anti-1,3-diols in several individual reactions by subjecting each of them to some practically viable metal-mediated Barbier-type allylations under moist conditions. In this regard, a detailed investigation was made regarding the compatibility and stereoselectivity associated with four such metal-mediated allylations of these aldehydes 5–7. Good yields with moderate selectivity in several successful reactions with easy chromatographic separation of diastereoisomers of the products have been elegantly exploited to isolate two pairs of enantiomerically pure syn-1,3 and anti-1,3-diols (6a and 6b; 10a and 10b) in substantial amounts. Finally, 10b has been exploited to synthesize (−)-galantinic acid A.

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(2R,3S)-1,2-O-Cyclohexylidine-3-tert-butyldiphenylsilyloxy-5-hexeneC28H38O3Si[α]D25=+15.3 (c 2.8, CHCl3)Source of chirality: d-mannitolAbsolute configuration: (2R,3S)

(2R,3S)-1,2-O-Cyclohexylidine-3-benzoyloxy-5-hexeneC19H24O4[α]D25=+11.45 (c 2.2, CHCl3)Source of chirality: d-mannitolAbsolute configuration: (2R,3S)

(2R,3S,5S)-1,2-O-Cyclohexylidine-1,2,3,5-tetrahydroxyoct-7-eneC14H24O4[α]D25=+10.4 (c 2.0, CHCl3)Source of chirality: d-mannitolAbsolute configuration: (2R,3S,5S)

(2R,3S,5R)-1,2-O-Cyclohexylidine-1,2,3,5-tetrahydroxyoct-7-eneC14H24O4[α]D25=+0.5 (c 1.2, CHCl3)Source of chirality: d-mannitolAbsolute configuration: (2R,3S,5R)

(2R,3S,5S)-1,2-O-Cyclohexylidine-3-O-benzoyl-1,2,3,5-tetrahydroxyoct-7-eneC21H28O5[α]D25=+10.5 (c 1.04, CHCl3)Source of chirality: d-mannitolAbsolute configuration: (2R,3S,5S)

(2R,3S,5R)-1,2-O-Cyclohexylidine-3-O-benzoyl-1,2,3,5-tetrahydroxyoct-7-eneC21H28O5[α]D25=+12.7 (c 1.76, CHCl3)Source of chirality: d-mannitolAbsolute configuration: (2R,3S,5R)

(2R,3S,5R)-1,2-O-Dibenzoyl-1,2,3,5-tetrahydroxyoct-7-eneC22H24O6[α]D25=+13.2 (c 4.78, CHCl3)Source of chirality: d-mannitolAbsolute configuration: (2R,3S,5R)

(2R,3S,5R)-1,2-O-Tribenzoyl-1,2,3,5-tetrahdrooxyoct-7-eneC29H28O7[α]D25=+19.1 (c 1.57, CHCl3)Source of chirality: d-mannitolAbsolute configuration: (2R,3S,5R)

(2S,3S,5R)-Azido-1,3,5-O-tribenzoyloxy-oct-7-eneC29H27O6N3[α]D25=+13.7 (c 1.2, CHCl3)Source of chirality: d-mannitolAbsolute configuration: (2S,3S,5R)