Abstract
1,3-Enynes are important building blocks in organic synthesis and also constitute the key motif in various bioactive natural products and functional materials. However, synthetic approaches to stereodefined substituted 1,3-enynes remain a challenge, as they are limited to Wittig and cross-coupling reactions. Herein, stereodefined 1,3-enynes, including tetrasubstituted ones, were straightforwardly synthesized from cis or trans-alkynylated oxiranes in good to excellent yields by a one-pot cascade process. The procedure relies on oxirane deprotonation, borylation and a stereospecific rearrangement of the so-formed alkynyloxiranyl borates. This stereospecific process overall transfers the cis or trans-stereochemistry of the starting alkynyloxiranes to the resulting 1,3-enynes.
Highlights
Lithiated oxiranes are useful intermediates in organic synthesis [1,2]
In this context and based on the pioneering work of Shimizu [6,7], and our experience on the metalation of alkynyloxiranes and reactivity studies of the so-formed alkynyloxirane anions [12,13], we explored the reaction of such anions with various boron derivatives in order to produce stereodefined α-enynes after Matteson-type rearrangement [14] and elimination [15] (Scheme 1)
The corresponding oxiranyllithium was sufficiently stable at −78 °C to be trapped by various phenylboronic esters 2
Summary
Lithiated oxiranes are useful intermediates in organic synthesis [1,2]. Such species can undergo different reactions, driven either by their carbanionic or carbenic behavior [3,4], leading to various products. The resulting borate intermediate afforded the tetrasubstituted enyne 3 in good to moderate yields, depending on the boronic ester’s nature (Table 1). The cis-configured compound cis-1b readily reacted with pinacol phenylboronate 2c under the conditions set up above, providing enyne 4 as the sole product in high yield (Table 2, entry 1).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
