METALATED 2-ALKENYLSULFOXIMINES - EFFICIENT SOLUTIONS FOR ASYMMETRIC D(3)-SYNTHONS

By starting from the 4,5-dihydro-1,2 lambda(6),3-oxathiazole 2-oxides 5 and 6 or their enantiomers, a number of enantiopure acyclic and cycl ic 2-alkenyl sulfoximines have been prepared. After deprotonation' wit h n-BuLi and transmetalation with chlorotris(isopropoxy)titanium chlor ide, these sulfoximines can be gamma-hydroxyalkylated to the correspon ding gamma-hydroxy vinyl sulfoximines with high diastereomeric excesse s (greater than or equal to 95% de) irrespective of the nature of the added aldehyde. The cyclopentenyl- and cyclohexenylsulfoximines 50a/51 a and 50b/51b are demonstrated as the first examples of highly enantio selective solutions for cyclic d(3)-synthons. From the X-ray structure s of 18e, 21, 59, and 62, it can be deduced that the S-S/R(S)-configur ed 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 chira l aldehydes (reagent control), although here the achievable stereocont rol depends on the relative configuration of the stereogenic centers i n the auxiliary. This is especially true for the cyclohexenylsulfoximi nes 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 ac id based auxiliary. In the case of this intramolecular matched situati on, the stereochemical preferences of the chiral aldehyde can be overc ompensated nearly completely. This mutual reinforcement of the two ste reogenic centers in the sulfoximine moiety accounts for the high degre e of reagent control (greater than or equal to 94% de in the acyclic s eries, greater than or equal to 95% de with the five-membered ring sys tems, and greater than or equal to 97% de with the cyclohexenylsulfoxi mines) achievable with these 2-alkenylsulfoximines.