Copper-Catalyzed Protoboration of 1,3-Diynes as a Platform for Iterative Functionalization

Abstract

This paper presents the protoboration of 1,3-diynes as a platform for the iterative functionalization of various groups on enynes and dienes. Synthetic approaches to targets with high complexity are directed toward using small, modular building blocks similar to a “Lego” construction using iterative chemistry and automated synthesis. Organoboron compounds are currently in the spotlight for achieving these goals. Here, we report an operationally simple, regioselective protoboration of 1,3-diynes using a mixed diboron reagent and Cu­(I)/phosphine catalyst to provide enynylboronates in good yields. Under similar conditions, diprotoboration of 1,3-diynes was also achieved to access bench-stable 1,4-diboryl-1,3-dienes in good yields and regioselectivities. The iterative coupling capabilities of the products have been demonstrated along with other downstream transformations offering a range of value-added skeletons.

Unlocking Diverse π-Bond Enrichment Frameworks by the Synthesis and Conversion of Boronated Phenyldiethynylethylenes

“…In this regard, integrating boron moiety into organic π-conjugated 1,3-enyne frameworks will further increase their structural diversity and synthetic application potential . Recently, transition-metal-catalyzed two-component reactions or transition-metal-free stereoselective hydroboration of 1,3-diynes have been developed, which provide an elegant strategy for the synthesis of trisubstituted boronated organic π-conjugated 1,3-enyne frameworks . However, to the best of our knowledge, the synthesis of tetrasubstituted boronated organic π-conjugated 1,3-enyne frameworks by three-component borylation reactions has not been well developed.…”

Regio- and stereocontrolled synthesis of borylated E-enynes, Z-enediynes and derivatives from alkenyl-1,2-bis-(boronates)

“…12 Boron-enyne is an important scaffold for the generation of enediyne systems. There are several reports in the literature on the synthesis of boryl-functionalized enynes catalyzed with metals such as Cu, Ni, Co and Pt [13][14][15][16][17][18][19][20] or with phosphine. 21 However, these reactions are neither regioselective nor stereoselective.…”

Selective synthesis of boron-substituted enynesviaa one-pot diboration/protodeboration sequence

“…18 A similar approach was applied by Ganesh, who used a mixed diboron reagent. 19 Recently, Santos et al reported the selective synthesis of ( Z )-1,3-enynes via the hydrolysis of borylenyne intermediates. 20 All the described protocols utilized multicomponent catalytic systems that were generated in situ or strictly maintained reaction conditions.…”

“…The synthesis of a regioisomer with the boryl group at the external C sp 2 carbon is more challenging and is limited only to three examples. 18,19,21…”

“…Several different approaches, such as organocatalytic, 16 radical 17 and TM-catalyzed borylations, [18][19][20][21][22] were applied to access enynylboronates. However, the latter is the most developed.…”