Chiral sulfur-functionalized

Chiral phosphoryl and sulfinyl groups are known as efficient auxiliaries in asymmetric synthesis. As reported below, their asymmetric induction in the a-posi-tion has been used to prepare chiral non-racemic organophosphorus compounds a-substituted by a sulfur function. Such compounds can also be obtained from their a-hydroxy analogues by OH-4 SR stereoselective transformation. 

This part concentrates mainly on the utility of chiral sulfoxides in asymmetric synthesis. The main advantage of sulfoxides over the other sulfur functions which are described in this review is indeed their chirality. Sulfoxides are chiral groups which are easy to introduce, easy to remove and give high asymmetric induction in many reactions. ... 

Yeast-catalyzed double-bond reductions with sulfur-functionalized prenyl derivatives have been reported39. The products are again bifunclional chiral C5 building blocks for optically active terpenes. In this case, the incubation times are unusually long (17-21 days). 

Ferrocenylmethylamine also functions as a chelating bidentate ligand, and the cyclometallated platinum complex contains a planar chirality. The complex with the cyclometallated (7V,A-dimethylamino)methylferrocene and methyl phenyl sulfoxide ligands 469 is obtained as a mixture of the two diastereomers having the planar chirality and chiral sulfur atom. ... 

Scheme 7.57 Epoxidation of aldehydes catalyzed with sulfur-functionalized chiral ionic liquid...

A great advantage of catalyst 24b compared with other chiral Lewis acids is that it tolerates the presence of ester, amine, and thioether functionalities. Dienes substituted at the 1-position by alkyl, aryl, oxygen, nitrogen, or sulfur all participate effectively in the present asymmetric Diels-Alder reaction, giving adducts in over 90% ee. The reaction of l-acetoxy-3-methylbutadiene and acryloyloxazolidinone catalyzed by copper reagent 24b, affords the cycloadduct in 98% ee. The first total synthesis of ewt-J -tetrahydrocannabinol was achieved using the functionalized cycloadduct obtained [23, 33e] (Scheme 1.39). 

Cyclic dithioketals and acetals represent another important class of sulfur containing chiral auxiliaries, which are available in chiral form by biooxidation. Biotransformations were performed on a preparative scale using whole-cells (wild type and recombinant) and isolated enzyme. Again, enantiocomplementary oxidation of unsubstituted dithianes (linear and cyclic, R = H) was observed when using and CPMOcomo (Scheme 9.28) [211,212]. Oxygenation of functionalized substrates (R = substituted alkyl) with gave preferably trans... 

Several secondary metabolites are dithiolanes, as for instance the allelochem-icals found in the tropical weed, Sphenoclea zeylanica. Zeylanoxide A is present in two stereoisomeric forms depending on whether the chirality at sulfur is (R) or (5) the latter form is 44 (Scheme 15). Zeylanoxides B are similar but in these cases the oxide function is on the sulfur at the 2 position. These molecules inhibited root growth in rice seedlings as well as the germination of letuce seeds.95... 

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