The effects of hydrogen-bonding organocatalysts and water for the acceleration of epoxide openings with a variety of nucleophiles are additive and lead to excellent yields of the catalyzed reactions in water.

We present a mild and efficient method for the completely regioselective alcoholysis of styrene oxides utilizing a cooperative Brønsted acid-type organocatalytic system comprised of mandelic acid (1 mol %) and N,N'-bis-[3,5-bis-(trifluoromethyl)phenyl]-thiourea (1 mol %). Various styrene oxides are readily transformed into their corresponding beta-alkoxy alcohols in good to excellent yields at full conversion. Simple aliphatic and sterically demanding, as well as unsaturated and acid-sensitive alcohols can be employed.

Consecutive ring-expansion reactions of oxiranes with dimethylsulfxonium methylide were studied experimentally and modeled computationally at the density functional theory (DFT) and second-order Møller-Plesset (MP2) levels of theory utilizing a polarizable continuum model (PCM) to account for solvent effects. While the epoxide to oxetane ring expansion requires 13-17 kcal mol(-1) activation and occurs at elevated temperatures, the barriers for the ring expansions to oxolanes are higher (ca. 25 kcal mol(-1)) and require heating to 125 °C. Further expansions of these oxolanes to the six-membered oxanes are hampered by high barriers (ca. 40 kcal mol(-1)). We observe the complete conservation of the enantiomeric purities for the nucleophilic ring expansions of enantiomeric 2-mono- and 2,2-disubstituted epoxides and oxetanes with dimethylsulfoxonium methylide. This is a convenient general approach for the high-yielding preparation of optically active four- and five-membered cyclic ethers from oxiranes.

Herein we shed light on the mechanism of the reaction of epoxides with ammonium thiocyanate to give the corresponding thiiranes in water, and we present a computational mechanistic model for this highly useful reaction.

Ring opening reactions O 0132Hydrophobic Amplification of Noncovalent Organocatalysis. -The effects of a hydrogen-bonding organocatalyst and water for the acceleration of epoxide openings with a variety of nucleophiles are investigated. Interestingly, these effects are additive, e.g. the reactions do not only proceed best in water, but the activity of the catalyst is amplified. High yields of the ring-opened products are obtained in this way. -(KLEINER, C. M.; SCHREINER*, P. R.; Chem. Commun. (Cambridge) 2006, 41, 4315-4317; Inst. Org. Chem., Justus-Liebig-Univ., D-35392 Giessen, Germany; Eng.) -M. Paetzel 09-041