Enantioselective synthesis of tarchonanthuslactone using proline-catalyzed asymmetric α-aminooxylation

A practical enantioselective synthesis of tarchonanthuslactone 1, an important natural product with a polyol unit, is described. The sequence of synthetic reactions involves proline-catalyzed α-aminooxylation and iodine-induced electrophilic cyclization as the chiral inducing steps.

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(+)-(S)-4-(Benzyloxy)butane-1,2-diolC11H16O3[α]D25=+5.0 (c 1, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (S)

(+)-(S)-4-(Benzyloxy)-2-hydroxybutyl methanesulfonateC12H18O5S[α]D25=+0.4 (c 0.5, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (S)

(−)-(S)-4-(Benzyloxy)-1,2-epoxybutaneC13H18O2[α]D25=+1.55 (c 1.1, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (S)

tert-Butyl(R)-1-(benzyloxy)hex-5-en-3-yl carbonateC18H26O4[α]D25=+33.3 (c 0.6, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (R)

(−)-(4S,6S)-4-[2-(Benzyloxy)ethyl]-6-(iodomethyl)-1,3-dioxan-2-oneC14H17IO4[α]D25=-3.1 (c 1.3, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (4S,6S)

(+)-(2S,4S)-6-(Benzyloxy)-1,2-epoxyhexan-4-olC13H18O3[α]D25=+8.0 (c 1.25, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (1S,4S)

(+)-(2R,4S)-6-(Benzyloxy)hexane-2,4-diolC13H20O3[α]D25=+3.0 (c 1, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (2R,4S)

(+)-(4S,6R)-4-[2-(Benzyloxy)ethyl]-2,2,6-trimethyl-1,3-dioxaneC16H24O3[α]D25=+4.0 (c 0.5, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (4S,6R)

(−)-(4S,6R)-2-(2,2,6-Trimethyl-1,3-dioxan-4-yl)ethanolC9H18O3[α]D25=-15 (c 0.4, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (4S,6R)

(−)-(5S,7R,2Z)-Ethyl-5,7-(isopropylidenedioxy)octenoateC13H22O4[α]D25=-23.5 (c 0.17, CHCl3)Source of chirality: proline-catalyzed α-asymmetric aminooxylationAbsolute configuration: (5S,7R)