Highly Stereo- and Regioselective Synthesis of (Z)-Trisubstituted Alkenes via 1-Bromo-1-alkyne Hydroboration−Migratory Insertion−Zn-Promoted Iodinolysis and Pd-Catalyzed Organozinc Cross-Coupling
摘要:
Hydroboration of 1-bromo-1-alkynes with dibromoborane followed by addition of 3 or 4 equiv of Me2Zn provides an efficient and selective route to (Z)-2-alkenyldimethylboranes (3) or (Z)-2-alkenylmethylzincs (4), respectively, which have been successfully applied to one-pot Suzuki (B-I) or Negishi (Zn-I) coupling in some less demanding cases. However, in more demanding cross-coupling reactions, only the use of either (Z)-2-alkenyliodides (5) or the alkenylzincs prepared from lithiation and then zincation of 5 proves to be highly satisfactory (Zn-II or Zn-III protocol). On the contrary, the corresponding organoboron coupling under B-II or B-III protocol appears to be less satisfactory. Preliminary studies indicate that certain substituents proximal to trisubstituted alkenes seriously affect the course of the desired alkenylboron crosscoupling.
Highly (≥98 %) Selective Trisubstituted Alkene Synthesis of Wide Applicability via Fluoride-Promoted Pd-Catalyzed Cross-Coupling of Alkenylboranes
作者:Ei-ichi Negishi、Tomas Tobrman、Honghua Rao、Shiqing Xu、Ching-Tien Lee
DOI:10.1002/ijch.201000051
日期:2010.12
to give trisubstitutedalkenes, i.e., (Z)‐β‐Me‐substituted 3‐i–3‐xi and (E)‐β‐Ph‐substituted 2b–i and 2b–ii. In all cases, each alkene product was formed in a ≥98 % stereoselectivity. The propyne‐based protocol nicely complements the widely used Zr‐catalyzed alkyne methylalumination–Pd‐catalyzed alkenylation by providing a highly stereoselective(≥98 %) route to (Z)‐Me‐substituted alkenes.
( Z ) -β-溴-1-丙烯基(频哪醇)硼烷 ( 4 ),最近通过 1-丙炔的溴硼化反应以 85% 的产率提供了 ≥98% 异构体纯的化合物,已转化为β-烷基-,芳基-和烯基取代的 ( Z )-2-甲基-1-烯基(频哪醇)硼烷 ( 2a ) 在大约。通过 Pd 催化的 Negishi 烯基化与合适的有机溴化锌,基于丙炔的产率为 75%。氟化物,尤其是n Bu 4 NF(TBAF) 或 CsF显着促进了先前缓慢且产率适中的β , β-二取代链烯基硼烷的Suzuki 烯基化,以得到三取代的烯烃,即(Z ) -β -Me-取代的3 - i - 3-xi和 ( E ) -β -Ph-取代的2b-i和2b-ii。在所有情况下,每种烯烃产物的立体选择性均≥98%。基于丙炔的方案通过提供高度立体选择性(≥98%)的途径(Z)-Me 取代的烯烃,很好地补充了广泛使用的 Zr 催化的炔烃甲基铝化-Pd 催化的烯基化。
Perfluorinated 1H-indazoles and hydrotris(indazol-1-yl)borates. Supramolecular organization and a new synthetic procedure to form scorpionate ligands
作者:Bianca K. Muñoz、Wilfried-Solo Ojo、Kane Jacob、Nuria Romero、Laure Vendier、Emmanuelle Despagnet-Ayoub、Michel Etienne
DOI:10.1039/c4nj00136b
日期:——
This paper describes the syntheses and full characterization of perfluorinated 1H-indazoles 2–5 and hydrotris(indazolyl)borate thallium complexes 6–9 that contain linear perfluoroalkyl chains varying from two to six carbon atoms in the 3-position. In the solid state, the perfluorinated 1H-indazoles exhibit supramolecular structures that depend on the length of the perfluoroalkyl chain. A catemer of