Hindered organoboron groups in organic chemistry. 25. The condensation of aliphatic aldehydes with dimesitylboryl stabilised carbanions to give alkenes.
作者:Andrew Pelter、Keith Smith、Said M.A. Elgendy
DOI:10.1016/s0040-4020(01)87983-7
日期:1993.8
In the presence of protic acids the condensation of aliphatic aldehydes with dimesitylboryl stabilised carbanions results in alkenes. In the presence of strong acids such as HCl or CF3SO3H, the products contain > 90% of E-alkenes in all cases tried. When acetic acid is used, then Z-alkenes may result predominantly, particularly in the cases of RsCHO and RtCHO. HX HCI, CF3SO3H gives E - alkenes in
在质子酸的存在下,脂族醛与二聚三苯甲基稳定的碳负离子的缩合会生成烯烃。在强酸(例如HCl或CF 3 SO 3 H)的存在下,在所有尝试的情况下,产品均含有> 90%的E-烯烃。当使用乙酸时,则可能主要产生Z-烯烃,特别是在R s CHO和R t CHO的情况下。在所有情况下,HXHCl,CF 3 SO 3 H均会生成E-烯烃。HXCH 3 CO 2 H,使得主要ž -烯烃当Rř秒,R叔。
The stereospecific hydrogenolysis of vinylic sulfones by sodium dithionite in a protic medium proceeds by addition of HSO2 to give an intermediate which could be isolated after alkylation in situ to a 1,2-bissulfone. The mechanism is therefore of the β-addition-elimination type. In the case of E-2-benzenesulfonyl-2-butene and ethyl iodide a single crystalline diastereoisomer was obtained and shown
Hydroindation of allenes and its application to radical cyclization
作者:Naoki Hayashi、Yusuke Hirokawa、Ikuya Shibata、Makoto Yasuda、Akio Baba
DOI:10.1039/b803314e
日期:——
Hydroindation of allenes and radical cyclization of 1,2,7-trienes (allenenes) were accomplished by HInCl2 with high regioselectivity to afford a variety of cyclic compounds. The resulting vinylic indiums could be used for successive coupling reactions in a one-pot procedure. The use of HInCl2 generated slowly in situ is extremely effective for the radical cyclization.
In the presence of HX, carbanions Mes2BCHLiR1 react with aliphatic aldehydes to give alkenes. The stereochemistry of the product alkene depends upon the nature of HX.
Ironing out the kinks: Efficientnew catalytic systems based on iron thiolates are described for the iron‐catalyzed cross‐coupling of alkyl Grignard reagents with alkenylhalides (see scheme). The reaction is highly chemo‐ and stereoselective. With this new procedure, the use of N‐methylpyrrolidone as a co‐solvent is no longer required.