Investigations on the Suzuki−Miyaura and Negishi Couplings with Alkenyl Phosphates: Application to the Synthesis of 1,1-Disubstituted Alkenes
摘要:
The development of versatile Suzuki-Miyaura and Negishi cross-couplings with nonactivated alkenyl phosphates and aromatic boronic acids or organozinc reagents was achieved in acceptable to good yields. A series of 1,1-disubstituted alkenes were synthesized using a combination of either Ni(COD)(2)/Cy3P/ K3PO4 or Pd(2)dba(3)/DPPF in THF. When working with alkenyl electrophiles in metal-catalyzed cross-couplings, this method lends itself as a less costly and more stable alternative to the corresponding triflate or nonaflate derivatives. In addition, initial studies are presented regarding an efficient 1,2-migration under Negishi coupling conditions.
Br-radical-mediated [3+2] annulation: synthesis of 2-bromomethyl-substituted alkenylcyclopentanes by the reaction of alkenylcyclopropanes with allyl bromides under photo irradiation
A radicalchain addition of allyl bromides 2 to alkenylcyclopropanes 1 resulted in [3+2] annulation to give 2-bromomethyl-alkenylcyclopentanes 3 in good yields (16 examples). In this reaction, two kinetically fast radicalreactions, cyclopropylcarbinyl radical-ring-opening and 5-exo-radical cyclization, preceded the β-fragmentation of a bromine radical to make the formal cycloaddition possible.