Total synthesis of avenaol

Motohiro Yasui,Chihiro Tsukano,Rina Ota,Yoshiji Takemoto

doi:10.1038/s41467-017-00792-1

Motohiro Yasui, Chihiro Tsukano + Show 2 more

Open Access

https://doi.org/10.1038/s41467-017-00792-1

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Abstract

Avenaol, isolated from the allelopathic plant black oat, was the first C20 germination stimulant related to strigolactones. Structurally, it consisted of a bicyclo[4.1.0]heptanone skeleton containing a cyclopropane ring bearing three main chains projecting in the same direction (i.e. all-cis-substituted cyclopropane). Herein, we report the total synthesis of avenaol using a robust strategy involving the formation of an all-cis-substituted cyclopropane via an alkylidenecyclopropane. The key factors in the success of this total synthesis include the Rh-catalysed intramolecular cyclopropanation of an allene, an Ir-catalysed stereoselective double-bond isomerisation, and the differentiation of two hydroxymethyl groups via the regioselective formation and oxidation of a tetrahydropyran based on the reactivity of a cyclopropyl group. This strategy effectively avoids the undesired ring opening of the cyclopropane ring and the formation of a caged structure. Furthermore, this study confirms the proposed structure of avenaol, including its unique all-cis-substituted cyclopropane moiety.

Highlights

The key factors in the success of this total synthesis include the Rh-catalysed intramolecular cyclopropanation of an allene, an Ir-catalysed stereoselective double-bond isomerisation, and the differentiation of two hydroxymethyl groups via the regioselective formation and oxidation of a tetrahydropyran based on the reactivity of a cyclopropyl group
We have achieved the total synthesis of avenaol
The key feature of this synthesis is the use of an alkylidenecyclopropane, which allowed for the robust formation of an all-cis-substituted structure via a stereoselective double-bond isomerisation and avoided the cleavage of the cyclopropane ring and the formation of a caged structure

Summary

Introduction

Avenaol, isolated from the allelopathic plant black oat, was the first C20 germination stimulant related to strigolactones It consisted of a bicyclo[4.1.0]heptanone skeleton containing a cyclopropane ring bearing three main chains projecting in the same direction (i.e. all-cis-substituted cyclopropane). The key factors in the success of this total synthesis include the Rh-catalysed intramolecular cyclopropanation of an allene, an Ir-catalysed stereoselective double-bond isomerisation, and the differentiation of two hydroxymethyl groups via the regioselective formation and oxidation of a tetrahydropyran based on the reactivity of a cyclopropyl group. This strategy effectively avoids the undesired ring opening of the cyclopropane ring and the formation of a caged structure. A variety of different strategies have been reported for the synthesis of typical SLs15–25, there have been no reports to date for the synthesis of avenaol

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Results

Conclusion