Stereoselective Syntheses of (+)-Goniodiol, (−)-8-Epigoniodiol, and (+)-9-Deoxygoniopypyrone via Alkoxyallylboration and Ring-Closing Metathesis

Abstract

A convenient synthesis of (+)-goniodiol, (-)-8-epigoniodiol, and (+)-9-deoxygoniopypyrone has been developed via asymmetric alkoxyallylboration and ring-closing metathesis pathways.

An Olefin Metathesis/Double Bond Isomerization Sequence Catalyzed by an In Situ Generated Ruthenium Hydride Species

“…The former route is a single‐step procedure that requires only one catalyst, but the reactivity of enol ethers B is significantly lower than allyl ethers E . The latter route has the advantages of using a smooth allyl ether metathesis11 and homoallylic alcohols F as starting materials, which are, in contrast to pentenols C , available in enantiomerically pure form by numerous methods, for example well‐established allylboration strategies 12. The disadvantage is obviously the additional double‐bond migration step ( A ⇄ D ), which can be mediated by stoichiometric amounts of strong bases or catalytic amounts of various transition metal complexes of rhodium,13a iridium,13b nickel13c and ruthenium 13d−13f.…”

Synthetic Studies Towards the Core Tricyclic Ring System of Pradimicin A

“…We planned to utilize the stoichiometric chiral allylborane 18 (Scheme 3) derived from α-pinene developed by Brown et al [40] This alkoxyallylboration can be applied to a wide range of aldehyde substrates, and the syntheses of several higher-order alkoxyallylboranes in situ are well known. [41] By using similar conditions with aldehyde 17, homoallylic alcohol product 19 was obtained in 66 % yield and 72 % ee (Scheme 3). [40] The 1,2-syn-alkoxy homoallylic alcohol products are obtained with high ee and dr.…”

Asymmetric Synthesis of Styryl-Lactones

“…A convenient synthesis of (+)-goniodiol (6), (-)-goniodiol (ent-6) and (+)-9-deoxy-goniopypyrone has been recently developed by Ramachandran et al [96] v i a asymmetric alkoxyallylboration and ring-closing metathesis pathways. Alkoxyallylboration of benzaldehyde with borane 2 2 2 , prepared in three steps from allyl methoxyethoxymethyl ether, gave the α-alkoxyhomoallylic alcohol 223 (98% e.e.)…”