dungen unter den jeweiligen Reaktionsbedingungen. Diese Forderung schrankt naturgeman die Auswahl moglicher Reagentien ein, da resonanzstabilisierte ,,Carbanionen" nur begrenztL8] konfigurativ stabil und a-acceptorsubstituierte, polare Organometallverbindungen mit einheitlicher absoluter Konfigurdtion am metallierten Kohlenstoff bislang in enantiomerenreiner Form unbekannt sindrgl. Als einen Ausweg aus dieser Situation schlagen wir hier die diastereoseitendifferenzierende Transmetallierung von konfigurativ labilen, enantiomerenreinen, lithiierten 2-Alkenylsulfoximiden 2 zu den homochiralen, konfigurativ stabilen (?) 2-Alkenyltitanverbindungen 3 bzw. 4 vor (Schema 1).Die als Ausgangsmaterial benotigten enantiomerenreinen Allylsulfoximide l lassen sich in hohen Ausbeuten mit Hilfe der von uns kiirzlich beschriebenen 4,5-Dihydro-1,2h6,3-oxathiazol-2-oxide 5 und epi-5, welche ihrereseits rnit 70 % Ausbeute aus 0-Trimethylsilylvalinol und p-Toluolsulfinsaurechlorid zuginglich sind, herstellen (Schema 2)['"].

By starting from the 4,5-dihydro-1,2λ6,3-oxathiazole 2-oxides 5 and 6 or their enantiomers, a number of enantiopure acyclic and cyclic 2-alkenyl sulfoximines have been prepared. After deprotonation with n-BuLi and transmetalation with chlorotris(isopropoxy)titanium chloride, these sulfoximines can be γ-hydroxyalkylated to the corresponding γ-hydroxy vinyl sulfoximines with high diastereomeric excesses (≥95% de) irrespective of the nature of the added aldehyde. The cyclopentenyl- and cyclohexenylsulfoximines 50a/51a and 50b/51b are demonstrated as the first examples of highly enantioselective solutions for cyclic d3-synthons. From the X-ray structures of 18e, 21, 59, and 62, it can be deduced that the S S/R S-configured sulfoximines attack the aldehydes nearly exclusively from their Re/Si faces, respectively. A remarkable property of these systems is that this stereochemical interrelation holds also for reactions with chiral aldehydes (reagent control), although here the achievable stereocontrol depends on the relative configuration of the stereogenic centers in the auxiliary. This is especially true for the cyclohexenylsulfoximines 50b and 51b, which require the same absolute configuration at both the sulfur atom and the carbon atom in the side chain of the amino acid based auxiliary. In the case of this intramolecular matched situation, the stereochemical preferences of the chiral aldehyde can be overcompensated nearly completely. This mutual reinforcement of the two stereogenic centers in the sulfoximine moiety accounts for the high degree of reagent control (≥94% de in the acyclic series, ≥95% de with the five-membered ring systems, and ≥97% de with the cyclohexenylsulfoximines) achievable with these 2-alkenylsulfoximines.

No abstract

A number of C 2 -symmetrical geminal bis-(sulfoximine)s have been prepared for the first time and used as ligands in boron-mediated reductions of acetophenone and copper complex-catalyzed 1,4-additions of diethylzinc to 2-cyclohexenone. The copper complex of bis(sulfoximine) 46 was found to be highly active in this type of reaction, furnishing the addition product in nearly quantitative yield even at À 90 8C. From the reaction of bis(sulfoximine) 42 with Cu(OTf) 2 a copper complex was isolated and characterized by X-ray structural analysis. A mixture of SES-Cl and NaN 3 in acetonitrile was found to behave like SES-N 3 in FeCl 2 -mediated iminations of sulfoxides, affording the corresponding sulfoximines with complete retention of the sulfur configuration.