Three-Component Borylallenylation of Alkynes: Access to Densely Boryl-Substituted Ene-allenes

Abstract

Ene-allenes serve as versatile building blocks in organic synthesis, and the development of their efficient preparation is valuable. Herein the synthesis of boryl-substituted ene-allenes utilizing a Cu/Pd-catalyzed borylallenylation of alkynes with propargylic carbonates and bis(pinacolato)diboron is reported. Densely (tetra-, penta-, and hexa-) substituted eneallenes were synthesized in acceptable yield with high regio-and stereoselectivity. More important molecule structures can be obtained by subsequent modifications.

Cu/Pd-Catalyzed cis-Borylfluoroallylation of Alkynes for the Synthesis of Boryl-Substituted Monofluoroalkenes

“…Simultaneously, the use of palladium catalysts with larger steric phosphine ligands is beneficial for the ring-opening coupling of gem- difluorinated cyclopropane. The combination of the two catalytic processes can be effectively connected in series . Herein, we describe the Cu/Pd dual-catalyzed cis- borylfluoroallylation of alkynes for the synthesis of boryl-substituted monofluoroalkenes (Scheme b).…”

“…Numerous studies have been conducted with the purpose of constructing valuable monofluoroalkene compounds. Methods for this process include Julia-Kocienski olefination, the Horner–Wadsworth–Emmons reaction, and the catalytic conversion of fluorinated building blocks. , More recently, the Pd-catalyzed C–C activation/C–F bond cleavage of readily available gem- difluorinated cyclopropane has been demonstrated as an efficient strategy for accessing monofluoroalkenes. , In view of the extremely efficient borylative difunctionalization of alkynes − and the importance of monofluoroalkene, we envision that a three-component reaction involving gem- difluorocyclopropane, alkynes, and bis­(pinacolato)­diboron (B 2 pin 2 ) may simplify the synthesis of new-generation boryl-monofluoroalkene compounds. The insertion of Cu–B into triple bonds can be easily realized by the use of Cu catalysts.…”

“…This proves that the diboron compound 13 is not an intermediate in the reaction. Integrating the results of the above mechanism experiments with those described in previous literature, , we propose the following mechanism (Scheme b). First, the Cu-catalyzed borylcupration of alkyne generates a borylalkenylcopper intermediate ( I ).…”

Copper-Catalyzed Borylative Difunctionalization of π-Systems

“…The resulting organocopper intermediate then undergoes an S N 2′-type oxidative addition to the allylic phosphate. Finally, reductive elimination generates the product (91) with preference for the branched product. The methodology was applied to the total synthesis of Rottnestol and Herboxidiene.…”

“…This dual metal approach garnered significant interest toward the development of other Pd/Cu borylallylation strategies. Notable contributions from Gong and Fu, 91 as well as Fanãnaś-Mastral 92 have illustrated methods utilizing alkynes as π-acceptors with allylic or propargylic alcohol derivatives (Scheme 30a), generating the boryl-functionalized skipped diene (114) or vinylallene (115) products. Fanãnaś-Mastral also examined the nature of the transmetalation by employing substrate 112c (Scheme 30b).…”