propargylations occurred under retention of configuration at the propargyliccenter. Most important for the diastereoselectivity of the nucleophilic trapping reaction is the configurational stability of the diastereotopic cation 4 as reflected by substituent effects. In situ ionizations according to an S(N)1-mechanism not only result in a considerable loss but also in an inversion of diastereoselectivity.
A synthesis of chiral flavanones via the condensation of tricarbonyl(h6-arylbenzaldehyde)chromium(0) and o-hydroxyacetophenone in a shorter time at room temperature have been developed. The tricarbonylchromium(0) group was removed by virtue of light and the enantioenriched flavanones was formed with highly enantioselectivity (> 95 % ee).
Arenetricarbonylchromium complexes as chiral auxiliaries: asymmetric synthesis of β-lactams
作者:Clara Baldoli、Paola Del Buttero
DOI:10.1039/c39910000982
日期:——
A new enantioselective synthesis of β-lactams via condensation of optically pure ortho-substituted benzylideneaminetricarbonylchromium complexes with ester-enolates is reported; the enantiomeric excess is higher than 98%.
The SmI(2)-induced cross-coupling of Cr(CO)(3)-complexed nitrones with carbonyl compounds is described. This highly chemo- and diastereoselective reaction affords enantiopure [small beta]-amino alcohol complexes in excellent yields.
Stereoselective synthesis of trans-2,6-diaryl-4-piperidones by using benzaldiminetricarbonylchromium derivatives
作者:Kaori Ishimaru、Takakazu Kojima
DOI:10.1039/b001540g
日期:——
Stereoselective synthesis of trans-2,6-diaryl-4-piperidones has been carried out by cycloaddition of benzaldiminetricarbonylchromium derivatives 1 with 2-silyloxybuta-1,3-diene in the presence of trimethylsilyl triflate as a Lewis acid. The tricarbonylchromium moiety played an important role in increasing the stereoselectivities of the products.