Catalytic S_N2′‐ and Enantioselective Allylic Substitution with a Diborylmethane Reagent and Application in Synthesis

Abstract

A catalytic method for site- and enantioselective addition of commercially available di-B(pin)-methane to allylic phosphates is introduced (pin = pinacolato). Transformations may be facilitated by an NHC-Cu complex (NHC = N-heterocyclic carbene) and products obtained in 63–95% yield, 88:12 to >98:2 SN2′:SN2 selectivity and 85:15–99:1 enantiomeric ratio. The utility of the approach, entailing the involvement of different catalytic cross-coupling processes, is highlighted by application to formal synthesis of cytotoxic natural product rhopaloic acid A.

Synthesis of Asymmetrical‐Terminally Bifunctionlized Alkanes by Sequential Suzuki–Miyaura Coupling Using B‐Thexylboracyclanes

“…On the other hand, unsymmetrical diboroylalkanes allow one to connect two building blocks through alkyl spacers of various lengths using different conditions. The alkyl spacer possessing a boronic acid derivative and a dialkylboryl group can be prepared by hydroboration of an alkenyl‐containing stable boronic acid derivative with dialkylboranes , . Molander and co‐workers have demonstrated a one‐pot hydroboration and bidirectional SMC of alkenyl‐containing organotrifluoroborates …”

Benzyltriboronates: Building Blocks for Diastereoselective Carbon–Carbon Bond Formation

“…4 Alkylboronates, typically synthesized by alkene hydroboration 5 or Miyaura-type borylation of alkyl halides, 6 are likewise valuable reagents for C–C bond formation whose utility will continue to grow as methods for C(sp 3 )–C(sp 3 ) cross coupling mature. 7 Polyboron compounds such as gem -diboronates are beginning to emerge as useful reagents for C–C bond formation as well and have been applied to alkylation reactions, 8 boron–Wittig olefinations, 9 1,2-additions to carbonyls 10 and imines, 11 addition to pyridine- N -oxides, 12 allylic substitution, 13 and enantioselective cross couplings. 14 The use of 1,1,1-alkyltriboronates for C–C bond formation offers similar, if not greater, potential but is less explored and limited to deborylative boron–Wittig olefination 15 or deborylative alkylation (Scheme 1A).…”

Versatile Homoallylic Boronates by Chemo‐, SN2′‐, Diastereo‐ and Enantioselective Catalytic Sequence of Cu−H Addition to Vinyl‐B(pin)/Allylic Substitution

“…By providing an efficient, chemo-, S N 2’-, diastereo- and enantioselective method for accessing otherwise difficult-to-prepare and readily alterable homoallylic boronate compounds, we provide further evidence regarding the importance of sulfonate-containing chiral NHC ligands. These Cu-based complexes have formerly proven optimal in catalyzing enantioselective allylic substitution reactions [24] and conjugate addition processes [15,25] with C-based nucleophiles as well as Cu–B(pin) additions to alkenes [26] and allenes; [27] this is however the first time that a member of this catalyst class has emerged as the most effective for enantioselective Cu–H additions to an alkene.…”