Aromatische Kohlenwasserstoffe geben mit Dichlormethyl‐alkyläthern bei Gegenwart von Friedel‐Crafts‐Katalysatoren in guten Ausbeuten die entsprechenden Aldehyde. Zur Darstellung der Chloräther im Labormaßstab wird ein einfaches Verfahren angegeben.

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Enantioselective epoxidation of prochiral allylic alcohols with optically active 4,6-di-0-acetyl-2,3-dideoxy-a-~-threo-hex-2-enopyranosyl hydroperoxide in the presence of Ti(o-i-P~-)~ gives chiral epoxy alcohols with moderate enantiomeric excess. KEY WORDS: asymmetric induction, capillary gas chromatography, cyclodextrin stationary phases Although organic hydroperoxides are useful oxidants for many organic compounds such as olefins, to our knowledge only quite recently have they been used as chiral oxidants for asymmetric epoxidation. ' Attempts to prepare homochiral hydroperoxides by oxidation of prochiral compounds with hydroperoxides, enzymatic methods, 3a.b,c or by chromatographic separation of the diastereomers after resolution processes4 have been described. Stable, enantiomerically pure hydroperoxides have also been obtained by oxidation of 2,3-unsaturated glycosides with hydrogen peroxide. Preliminary experiments showed that the oxidation of sulfides to sulfoxides gave low (5%) asymmetric inductions. MATERIALS AND METHODSReagents The hydroperoxide 1 was prepared as described in a previous paper. General ProcedureA mixture of an allylic alcohol (1 mmol), the hydroperoxide 1 (1 mmol), and Ti(0-i-Prl4 (0.1 mmol) in dry CH2C12 was stirred at 0°C. After 8 h the conversion of the allylic alcohol was about 50% and the corresponding amount of epoxy alcohol was formed as determined by GLC on a Carbowax 20M column. The e. e. of the epoxy alcohol formed was estimated in the resulting mixture by GLC on cyclodextrin chiral stationary phases.6 Peak assignment to the R and S configuration of RESULTS AND DISCUSSIONHere, we report on the enantioselective epoxidation of some allylic alcohols with the optically pure 4,6-di-O-acetyl-2,3-dideox-a-~-threo-hex-2-enopyranosyl hydroperoxide Allylic alcohols have been epoxidized by 1 in the presence of Ti(0-i-Pd4 in CH& according to Scheme 1. After about 50% conversion of the allylic alcohol the enantiomeric excess (e.e.) of the epoxy alcohols formed has been estimated in the reaction mixture by gas chromatography on cyclodextrin chiral stationary phases (Figs. 1 and 2h6 The results obtained for a few allylic alcohols are summarized in Table 1.As shown in Table 1 the absolute configuration of the excess enantiomer is (+)-(R) and (-)-(2S,3R) in the case of 1-octen-3-01, respectively.We have found moderate optical inductions (20% e.e.) in the reaction with ally1 alcohol and 2-methyl-3-buten-2-01. Best results have been obtained with 3-methyl-2-buten-1-01 (more

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