Enantiospecific Alkynylation of Alkylboronic Esters.
Enantioenriched secondary and tertiary alkyl pinacolboronic esters undergo enantiospecific deborylative alkynylation through a Zweifel-type alkenylation followed by a 1,2-elimination reaction. The process involves use of α-lithio vinyl bromide or vinyl carbamate species, for which application to Zweifel-type reactions has not previously been explored. The resulting functionalized 1,1-disubstituted alkenes undergo facile base-mediated elimination to generate terminal alkyne products in high yield and excellent levels of enantiospecificity over a wide range of pinacolboronic ester substrates. Furthermore, along with terminal alkynes, internal and silyl-protected alkynes can be formed by simply introducing a suitable carbon- or silicon-based electrophile after the base-mediated 1,2-elimination reaction.
['Wang|Yahui|Y|', 'Noble|Adam|A|', 'Myers|Eddie L|EL|', 'Aggarwal|Varinder K|VK|http://orcid.org/0000-0003-0344-6430']
alkynylation alkynes boronic esters synthetic methods