Stereodivergent Construction of Vicinal Acyclic Quaternary–Tertiary Carbon Stereocenters by Michael-Type Alkylation of α,α-Disubstituted <i>N</i>-<i>tert</i>-Butanesulfinyl Ketimines
作者:Nuermaimaiti Yisimayili、Hui Liu、Yun Yao、Chong-Dao Lu
DOI:10.1021/acs.orglett.1c02660
日期:2021.10.1
constructed with excellent stereoselectivity via aza-enolization of enantioenriched acyclic N-tert-butanesulfinyl ketimines bearing two sterically similar α-linear alkyl substituents followed by conjugate addition to nitroalkenes. Further changes of the absolute configuration of the sulfinyl group and/or the α-stereocenter in the ketimine allowed the facile stereodivergent synthesis of all four diastereomers
Enantioselective Synthesis of 6-nor-Fluvirucinin B<sub>1</sub>
作者:Franz Bracher、Anne W. Baltrusch
DOI:10.1055/s-2002-34214
日期:——
An enantioselective synthesis of the 6-nor-derivative 3 of the antiviral macrocyclic lactam fluvirucinin B1 (2) is presented. Key steps are two regioselective ring opening reactions of chiral epoxides, and a ring-closing metathesis with Grubbs’ catalyst. The choice of appropriate protective groups was essential for the success and efficiency of the synthesis.
Assignment of stereochemistry in the oligomycin/rutamycin/cytovaricin family of antibiotics. Asymmetric synthesis of the rutamycin spiroketal synthon
作者:David A. Evans、Dale L. Rieger、Todd K. Jones、Stephen W. Kaldor
DOI:10.1021/jo00313a011
日期:1990.12
The absolute stereochemistry of the rutamycin antibiotics 2a,b has been established through asymmetric synthesis of the known degradation product 4. One of the key steps in the assemblage process involves acylation of the metalated hydrazone 6 with the N-methoxy-N-methyl amide 5. Both of these enantiomerically pure intermediates have been prepared in good overall yield and high diastereoselectivity (de > 94%). All absolute stereochemical relationships were established through alkylation and aldol bond constructions using N-acyloxazolidinone chiral auxiliaries. Subjection of 17 to acid hydrolysis/deprotection resulted in loss of protecting groups and subsequent spiroketalization to 19 (80%). Silylation of the secondary alcohol in 19 was followed by a samarium-catalyzed Meerwein-Ponndorf-Verley reduction to provide the equatorial alcohol 20 in excellent yield and stereoselectivity (de = 97%). Control experiments indicate that this surprisingly stereoselective reaction operates under kinetic control and that the observed stereochemical outcome may be the result of coordination of the reactive reducing agent to the axial spiroketal oxygen. Conversion of 20 to triol 4 afforded material that is identical with the rutamycin degradation product in all respects. These results establish that the absolute stereochemistry of the rutamycins is as shown (2a,b).