Total synthesis of two novel brominated acetylenic diols (+)-diplyne C and E: stereoselective construction of the (E)-1-bromo-1-alkene

The total syntheses of the enantiomers of two novel brominated polyacetylenic natural products diplynes C and E are reported. Pd and Cu(I)-catalyzed coupling reactions were employed to synthesize the diyne and enyne units. The stereochemistry of the terminal (E)-alkenyl bromide in diplyne C was constructed stereoselectively using Brown’s hydroboration–bromination procedure. The stereochemistry of the internal (E)-double bond in diplyne E was established using a Takai reaction. The stereocenter was derived from d-mannitol.

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(+)-(S)-Diplyne CC16H23BrO2Ee = >98%[α]D = +13.3 (MeOH)Source of chirality: d-mannitolAbsolute configuration: 2S

(+)-(S)-Diplyne EC16H17BrO2Ee = >98%[α]D = +5.9 (c 0.15, MeOH)Source of chirality: d-mannitolAbsolute configuration: 2S

4-(14-Bromo-tetradec-13-ene-1,3-diynyl)-2,2-dimethyl-[1,3]dioxolaneC19H27BrO2Ee = >98%[α]D = +28.6 (MeOH)Source of chirality: d-mannitolAbsolute configuration: 2S

9-(2,2-Dimethyl-[1,3]dioxolan-4-yl)-nona-6,8-diyn-1-olC14H20O3Ee = >98%[α]D = +42.9 (c 1.1, MeOH)Source of chirality: d-mannitolAbsolute configuration: 2S

9-(2,2-Dimethyl-[1,3]dioxolan-4-yl)-nona-6,8-diynalC14H18O3Ee = >98%[α]D = +33.7 (c 0.5, MeOH)Source of chirality: d-mannitolAbsolute configuration: 2S

12-Iodo-dodec-11-ene-3,5-diyne-1,2-diolC12H15IO2Ee = >98%[α]D = +8.9 (c 0.6, MeOH)Source of chirality: d-mannitolAbsolute configuration: 2S

14-Triisopropylsilanyl-tetradec-11-ene-3,5,13-triyne-1,2-diolC23H36O2SiEe = >98%[α]D = +8.2 (c 0.4, MeOH)Source of chirality: d-mannitolAbsolute configuration: 2S

Tetradec-11-ene-3,5,13-triyne-1,2-diolC14H16O2Ee = >98%[α]D = +6.1 (c 0.1, MeOH)Source of chirality: d-mannitolAbsolute configuration: 2S