Transition‐Metal‐Free Diboration Reaction by Activation of Diboron Compounds with Simple Lewis Bases

Abstract

Wechselnde Vorlieben: Durch die Wechselwirkung eines Tetraalkoxydiborans mit einer Lewis‐Base entsteht eine nukleophile Boryleinheit vom sp2‐Carbentyp, die nichtaktivierte CC‐Bindungen angreifen kann. Laut Computerstudien überlappt die stark polarisierte B‐B‐σ‐Bindung (HOMO) mit dem antibindenden π*‐Orbital (LUMO) der CC‐Bindung. Das normalerweise elektrophile Bor wird dabei nukleophil und zwingt das Olefin, sich wie ein Elektrophil zu verhalten.

Copper‐Catalyzed Alkynylboration of Alkenes with Diboron Reagents and Bromoalkynes

“…When alkynylborane (11)w as subjected to the optimizedr eaction conditions for 4-vinylbiphenyl, 3a was not produced. [14] Then, bis(borylated) derivative ( 12)w as subjected to the reaction, without obtaining the 3a.T hese observations exclude the possibility that bis(borylated) or alkynylborane derivatives were intermediates in the alkynylboration of alkenes. [15] On the basis of these experiments, apossible reactionmechanism was proposed (Scheme 6).…”

Transition-metal-free synthesis of imidazobenzothiazines via domino C-S/C-N bond formation

“…CuBr, CuCl, Cu(OAc) 2 , CuO, and CuSO 4 were found to be efficient catalysts for the tandem C-S/C-N reactions, while CuI gave the best result (Table 1, entries 1-7). In view of recent advances in transition-metalfree reactions [4][5][6][7][8][9][10][11][12][13][14][15], we intentionally performed this reaction without any copper salt as catalyst, and we surprisingly found that the desired product was also obtained ( Table 1, entry 8). We then changed K 2 CO 3 to Na 2 CO 3 , but lower yield was encountered (Table 1, entry 9).…”

“…Early in 2001, Beller first reported a transition-metalfree intra-and intermolecular C-N coupling with aryl chlorides with primary and secondary amines as substrates [4]. Thereafter, a great number of C-X coupling reactions have been developed into transition-metal-free reactions [5][6][7][8][9][10][11][12][13][14][15].…”

Singular Metal Activation of Diboron Compounds

“…However, the progress in this field has opened a new window toward the activation of tetra(alkoxy) diboron compounds in a metal-free context by the formation of Lewis acid-base adducts [167][168][169][170][171][172][173][174][175] and their addition to unsaturated substrates can be performed with total chemo-, regio-, and stereoselectivity. Therefore, this historical prospection toward the activation of diboron has moved from direct reaction of Cl 2 B-BCl 2 with alkenes to the current methodology that circumvent the activation of tetra(alkoxy)diboron reagents with simple LBs.…”