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。
Hindered organoboron groups in organic chemistry. 24. The condensation of aliphatic aldehydes with dimesitylboron stabilised carbanions to give ketones.
作者:Andrew Pelter、Keith Smith、Said M.A. Elgendy、Martin Rowlands
DOI:10.1016/s0040-4020(01)87982-5
日期:1993.8
The condensation of boron stabilised carbanions, Mes2BCHLiR1, (R1≠H) with aliphatic aldehydes, R2CHO, followed by treatment with trifluoroacetic anhydride (TFAA) or N-chlorosuccinimide (NCS) is an unique, broadly applicable redox process that yields ketones, R1CH2COR2, directly and in high yields. The anion Mes2BCH2Li (Mes2BCHLiR1, R1H) gives high yields of alkenes, R2CHCH2 in the same conditions
Carbanions of alkanesulfonyl halides and esters react with nonenolizable carbonyl compounds to give olefins. Mechanistic studies reveal that initial aldol-type addition of the carbanions is followed by cyclization–fragmentation to alkenes, and the leaving group on the sulfonyl moiety (RSO2X) controls carbanion stability and rate of the olefin formation.