Mechanisms of the synthesis of trialkylsubstituted alkenylboronates from unactivated internal alkynes catalyzed by copper: A theoretical study

Regio- and Stereoselective Synthesis of Multi-Alkylated Allylic Boronates through Three-Component Coupling Reactions between Allenes, Alkyl Halides, and a Diboron Reagent

“…Although the activation barriers of the coordination steps prior to the borylcuprations are generally small, and even negligible in many cases, this relative energy profile suggests that the coordination step could be a regio-and stereodetermining step. 84,85 We envisioned that the substituents R 1 and R 2 , which are perpendicular to the double bond where the borylcupration proceeds, can cause steric repulsion toward the boryl copper(I) species in the case of gem-disubstituted allenes. For the path of the experimental major isomer, (E)-4, the intermediate state EQ2 allyl-E is energetically higher than the precursor state EQ1, while the product state, alkenyl copper(I) Int3 allyl-E , is relatively stable (EQ2 allyl-E : ΔG = 12.4 kcal/mol; Int3 allyl-E : ΔG = −25.3 kcal/mol).…”

“…The respective transition states of the borylcupration ( TS2 ) for the four regio- and stereoisomers were successfully located 16–21 kcal/mol higher than the precursor state EQ1 , which consists of boryl copper­(I) species Int2 and the substrate 1a ( EQ1 : Δ G = 0.0 kcal/mol). It should be noted that, during the calculation of TS2 , we found that the transition states for the coordination of allene 1a to Int2 ( TS1 s) are comparable to those of the TS2 s. Although the activation barriers of the coordination steps prior to the borylcuprations are generally small, and even negligible in many cases, this relative energy profile suggests that the coordination step could be a regio- and stereodetermining step. , We envisioned that the substituents R 1 and R 2 , which are perpendicular to the double bond where the borylcupration proceeds, can cause steric repulsion toward the boryl copper­(I) species in the case of gem -disubstituted allenes. For the path of the experimental major isomer, ( E )- 4 , the intermediate state EQ2 allyl‑ E is energetically higher than the precursor state EQ1 , while the product state, alkenyl copper­(I) Int3 allyl‑ E , is relatively stable ( EQ2 allyl‑ E : Δ G = 12.4 kcal/mol; Int3 allyl‑ E : Δ G = −25.3 kcal/mol).…”

Copper-Catalyzed Ring-Opening Reactions of Alkyl Aziridines with B2pin2: Experimental and Computational Studies

“…Lin et al in 2002 isolated a series of nickel(II) azametallacyclobutanes from the reaction of several alkyl N -tosyl aziridines (with also a XRD structure) with Ni(bpy)(cod) or NiEt 2 (bpy), which could be consistent with the particular adduct needed in order to rationalize our borylation process [ 27 ]. On this basis, we initially hypothesized a simple model ( Scheme 4 ) in which the borylation is preceded by the opening of the protected aziridine to give rise to a four-membered azacopper intermediate I1 , which promoted the successive borylation [ 28 ].…”