The synthesis of new chiral hypervalent iodine compounds 3 and their use in asymmetric oxidative functionalizations are described. The substituents in the chiral moiety and the stereoelectronic properties of the reagents 3, as well as the reaction conditions, have been optimized. Chiral hypervalent iodine compounds 3 have been investigated in the asymmetric dioxytosylation of styrene and in the α-oxytosylation of propiophenone as test reactions. X-ray structural analysis of some reagents shows an interaction between the chiral moiety and the iodine resulting in stereoselectivities up to 53% ee in the products.

A series of ortho-substituted chiral hypervalent iodine reagents has been synthesized utilizing a zirconium-mediated iodoacylation reaction, which was followed by a stereoselective reduction, methylation, and an oxidation/ligand-exchange sequence. The evaluation of these new compounds as stereoselective electrophilic reagents towards alkenes and ketones is reported. Enantioselectivities as high as 65% have been achieved in the dioxytosylation of styrene and of up to 40% in the oxytosylation of propiophenone. X-ray structure

No abstract

AbstractsThe reaction of 4 with nitriles yields imine derivatives which subsequently react with different electrophiles (El = H, I, S) and are hydrolysed to the corresponding ketones 5 . With respect to R¢ and R¢¢ anti Friedel Crafts acylation product can be obtained in good yields (> 50 %). Access to 2,3-dihydroindoles 6 by reaction of 4 with allyl amines is very easy and good yields are obtained (65 -70 %). The two iodo substituents allow a variety of further transformations. 5Regioisomeric control of the insertion of trialkylsilylacetylene is high (>20 : 1). Subsequent reaction with sulfur dichloride and treatment with tetrabutylammonium fluoride yields polysubstituted benzothiophenes 7 .Besides dihydrofurans, other heterocyclic alkenes either with nitrogen or oxygen as heteroatoms and different ring sizes react with 3 and show excellent enantiomeric excesses and yields. 6Moreover Buchwald and coworkers published the stereoselective synthesis of allylic amines by using optically pure 3. 7Although chemistry with arenes has a long tradition in organic synthesis, the use of transition metal containing reagents can lead to completely new reactivities and therefore to new functionalization strategies. One of the first syntheses of an aryne zirconocene complex of type 4 was published by Erker et al. 1Bis(cyclopentadienyl)zirconium dichloride 1 is a commercially available and stable compound. It reacts in transmetallation reactions, either with t-BuLi, followed by a rearrangement to 2a, or with trimethylaluminium, to 2b. 2 Treatment of 2 with a lithiated arene results in zirconocene aryne complexes of type 4. They react with different alkenes and alkynes yielding 1,2 bis-functionalized arenes.3 The complexation and insertion properties of chiral zirconium compounds of type 3 with alkenes can also be used in stereoselective reactions. Preparation:The first synthesis and resolution of (rac)-(ebthi)ZrCl 2 (ebthi = ethylenebis(tetrahydroindenyl) was described by Brintzinger and coworkers. SYNLETT Spotlight 3This feature focuses on a reagent chosen by a postgraduate, highlighting the uses and preparation of the reagent in current research

1999 stereochemistry stereochemistry (general, optical resolution) O 0030 -034New Chiral Hypervalent Iodine Compounds in Asymmetric Synthesis.-Some new compounds of type (VI) are prepared and their use as electrophilic reagents in the asymmetric dioxytosylation of styrene and in the α-oxytosylation of propiophenone is reported. Up to 53% e.e. are obtained for the most effective iodine compound (VIa). The X-ray structural analysis of one iodine compound shows a strong interaction of the oxygen of the methoxy group and the iodine. -(HIRT, URS H.; SPINGLER, BERNHARD; WIRTH, THOMAS; J. Org. Chem. 63 (1998) 22, 7674-7679; Inst. Org. Chem., Univ. Basel, CH-4056 Basel, Switz.; EN)