Homoallenylboration of carbonyl compounds using inert 2-pinacolateboryl 1,3-butadienes via in situ generated borinic–TFA mixed anhydrides: efficient synthesis of homoallenyl alcohols

Abstract

A novel homoallenylboration reaction for the efficient and practical synthesis of valuable homoallenyl alcohols is presented. The reaction is initiated by the in-situ activation of inert 2-pinacolateboryl 1,3-butadienes via the...

Catalyst‐Free Propargylboration of Ketones with Allenyl‐Bpins: Highly Stereoselective Synthesis of tert‐Homopropargyl Alcohols Bearing Vicinal Stereocenters

“…and TFAA (1.2 equiv.) to a solution of 1 a in THF-d 8 at À 78 °C (Scheme 5a, path a), which resulted in two new signals at 47 ppm and 33 ppm in the 11 B NMR spectrum corresponding to the formation of 1 a-borinic ester [8a,b] and a small amount of byproduct n BuBpin, [10,12] respectively. Subsequently, 2 a (1.5 equiv.)…”

“…), two new signals at 49 ppm and 33 pm were observed in the 11 B NMR spectrum (Scheme 5b). Based on our pervious study, [10] the formation of borinic-TFA mixed anhydride 6 was likely implemented through a rapid exchange reaction between 1 aborinic ester and excess TFAA. The reactivity of 6 was further augmented in comparison to that of 1 a-borinic ester owing to the significant electron-withdrawing effect exerted by the TFA group.…”

“…Very recently, our research group made an intriguing discovery regarding the homoallenylboration of carbonyls using inert 2-pinacolateboryl 1,3-butadienes through the in-situ generation of borinic-TFA mixed anhydrides. [10] A primary mechanistic investigation revealed that highly reactive borinic-TFA mixed anhydrides could be formed in the reaction via a subsequent exchange reaction between the in-situ generated borinic ester and excess TFAA. Herein, we demonstrate that the exceptionally reactive nature of borinic-TFA mixed anhydride can be effectively utilized for catalyst-free propargylboration of ketones with allenyl-Bpins.…”