94719-35-4

An efficient kinetic resolution ofN-aryl β-amino alcohols has been developedviaasymmetricpara-aminations of anilines with azodicarboxylates enabled by chiral phosphoric acid catalysis. Broad substrate scope and high kinetic resolution performances were afforded with this method. Control experiments supported the critical roles of the NH and OH group in these reactions.

We report the direct preparation of 1,3-amino alcohols that contain up to three contiguous stereogenic centers by the umpolung coupling of imines and epoxides. Nucleophilic 2-azaallyl anions, generated from imines, are stereoselectively added to epoxides to furnish 1,3-amino alcohols after hydrolysis of the product imine. Transformations afford amino alcohols with >98% site selectivity with respect to both reaction partners and in up to >98% yield and >20:1 dr.

Recombinant Escherichia coli expressing a styrene monooxygenase, StyAB2, from Pseudomonas sp. LQ26 was applied to synthesize a range of chiral epoxides from conjugated styrene derivatives with excellent (>99%) enantioselectivity in most cases. The substrate preference was studied with a special focus on the steric effect of α- and β-substituents.

Triphenylarsine catalyses the formation of epoxides from carbonyl compounds and tosylhydrazone salts. This convergent synthesis gives complete trans selectivity for all aldehyde and tosylhydrazone salt coupling partners.

A novel, neutral catalytic cycle for the synthesis of epoxides from carbonyl compounds and diazo compounds using catalytic quantities of transition metal salts and sulfides has been developed.In this catalytic cycle, the diazo compounds is decomposed by the transition metal salt to give a metallocarbene, and this is picked up to the sulfide to give a sulfur ylide, which then reacts with the aldehyde to give an epoxide and returns the sulfide back into the catalytic cycle.To obtain good yields of epoxides it is necessary to maintain a low concentration of the diazo compound (by slow addition), otherwise dimerisation of the diazo compound is the dominant reaction.Factors affecting the outcome of the reaction were studied.The reactions are relatively insensitive to solvent, but are sensitive to the structure of the sulfide, the metal salt and the concentration.Unhindered sulfides give good yields of epoxides with any metal salt, but with hindered sufides higher yields are obtained with Cu(acac)2 than with Rh2(OAc)4.The yields of epoxides are sensitive to sulfide concentration especially when using substoichiometric amounts of sulfides.Higher concentration leads to faster rates of formation and subsequent reaction of the sulfur ylides, and consequently to higher yields.This novel catalytic cycle has also been applied to base-sensitive aldehydes.We found that our new catalytic cycle for epoxidation gives much improved yields of epoxides compared to those obtained by traditional sulfur ylide chemistry and is tolerant to a wide variety of sensitive functional groups.Ketones also participate in the catalytic cycle, although they give reduced yields of epoxides compared to aldehydes and require a slightly elevated temperature. - Keywords: catalysis; diazo compounds; epoxidations; sulfur ylides; synthetic methods

The -sigmatropic rearrangement of sulfur ylides derived via the desilylation of several α-trimethylsilylbenzyl sulfonium salts has been studied.The initally formed ylide was found to rapidly equilibrate with the thermodynamically more stable ylide.In the absence of trapping reagents, a Sommelet-Hauser type rearrangement occurs.

Oxidation of styrene, α- and β-alkyl-substituted styrenes, cis- and trans-stilbene, triphenylethylene, allylbenzene, and its trans β-alkyl-substituted derivatives with O(3P) resulted mainly in epoxides and carbonyl compounds formed by 1,2-H shifts.The O(3P) atoms were produced by microwave discharge of O2, CO2, or N2O/N2 in the presence of He.The temperature effect on the relative yields of products was studied on cis-stilbene and the regioselectivity of the O(3P) attack on the double bond in the series of β-alkylstyrenes and β-alkyl-substituted allylbenzenes.The mechanism of the oxidation is postulated to involve a diradical intermediate.The temperature effect is explained by the interconversion of different electronic states of this diradical and the steric effect by an early unsymmetric transition state for the addition of O(3P) atoms to the double bond.

The -sigmatropic rearrangement of sulfur ylides derived via the desilylation of several α-trimethylsilyl benzylsulfonium salts has been studied.The initially formed ylide was found to rapidly equilibrate with the thermodynamically more stable ylide.In the absence of trapping reagents, a Sommelet-Hauser-type rearrangement occurs.

Reduction of α-methylthio and α-phenylthio ketones 1 with L- selectride gave syn-alcohols 2 in high stereoselectivity except when R1 was cyclohexyl group, while reduction with Zn(BH4)2 gave the isomeric anti-alcohols 3 provided R3 was a methyl group.

Alkylation of α-methylthio or α-phenylthio ketones 1 with trimethyloxonium tetrafluoroborate and the reduction of the resulting sulfonium salts 5 with NaBH4 followed by the base treatment afforded trans epoxides 8 with high stereoselectivity.