[n]Dendralenes as a Platform for Selective Catalysis: Ligand-Controlled Cu-Catalyzed Chemo-, Regio-, and Enantioselective Borylations

Abstract

We report the development of two complementary methods for the Cu-catalyzed anti-Markovnikov borylation of one specific olefin in 2-substituted [n]­dendralenes (n = 3–6). The first protocol operates with a bisphosphine ligand and occurs with high regio- and chemoselectivity for the terminal double bond, independently of the number of cross-conjugated alkenes. We show that the use of a chiral phosphanamine ligand enables the highly chemo-, regio-, and enantioselective borylation of the alkene cross-conjugated with the terminal olefin in [n]­dendralenes.

Organophosphates as Versatile Substrates in Organic Synthesis

“…The same research group adopted an identical methodology to synthesize [n]dendralenes by the Kumada reaction of vinyl phosphate 7 – 2 ( Scheme 7 ) [ 56 ]. In this process, readily available phosphate 7 – 2 was subjected to a reaction with related Grignard reagents under different conditions.…”

Cross-Coupling of Ketone Enolates with Grignard and Zinc Reagents with First-Row Transition Metal Catalysts

“…53 After the work of Sherburn et al on [n]dendralenes, Mazet et al reported a modular synthetic route to access 2substituted [n]dendralenes using a Ni-catalyzed Kumada cross-coupling protocol for the synthesis of 2-substituted 1,3-dienes (Scheme 41). 52,54 The starting dienol phosphate was prepared in high yield by treatment of 3-phenylbut-3-en-2-one with LDA at −78 °C, followed by addition of diethyl chlorophosphite (1.5 equiv). With the [NiCl 2 (dmpe)] as catalyst, dienyl phosphates were cross-coupled with different vinylmagnesium bromide reagents leading to the desired [n]dendralenes from low to satisfactory yields.…”

Access to Cyclic Borates by Cu-Catalyzed Borylation of Unactivated Vinylcyclopropanes

“…The Cu-catalyzed borofunctionalization of π systems has emerged as an enabling approach for installing a C–B bond and simultaneously a vicinal C–H, C–C, or C–heteroatom bond across readily accessible unsaturated systems . Because of the central role of organoboron compounds, the growing interest observed for this strategy stems from the rapid access it offers to polyfunctional frameworks containing contiguous sp 2 - or sp 3 -hybridized carbon atoms using a nontoxic earth-abundant metal. , The commonly admitted mechanism for these reactions involves migratory insertion of a Cu–boryl species across the π system followed by trapping of the alkyl–copper intermediate by an electrophile and subsequent demetalation. , To date, diversely substituted cyclic and linear alkenes, 1,3-dienes, allenes, alkynes, enynes, and even dendralenes have been engaged in Cu-catalyzed borofunctionalization reactions. ,, These have been combined with more than 20 different electrophiles, including alkyl halides, aryl halides, aldehydes, ketones, imines, carbon dioxide, amines, or isocyanates, to name just a few (Figure A).…”

“… 3 , 4 To date, diversely substituted cyclic and linear alkenes, 1,3-dienes, allenes, alkynes, enynes, and even dendralenes have been engaged in Cu-catalyzed borofunctionalization reactions. 1 , 3 , 5 These have been combined with more than 20 different electrophiles, including alkyl halides, aryl halides, aldehydes, ketones, imines, carbon dioxide, amines, or isocyanates, to name just a few ( Figure 1 A).…”