Csaba Nemes

Enantioselective epoxidation of 2,2-dimethyl-2H-chromenes by dimethyldioxirane and jacobsen's Mn(III)salen catalysts

Enantioselective epoxidation of 2,2-dimethyl-2H-chromenes 1a-d has been performed by the Mn(III)salen complexes (R,R)-3 and (S,S)-3 as catalysts and dimethyldioxirane (DMD) as oxygen donor. The epoxychromans 2a-d were obtained in good yields and high enantioselectivities (up to 93% e.e.), which constitute the first examples of enantioselective epoxidation by DMD with the Jacobsen catalyst.

DIOXIRANE OXIDATION OF (Z)-1-THIOAURONES, (E)-3-ARYLIDENE-1-THIOCHROMAN-4-ONES AND (E)-3-ARYLIDENE-1-THIOFLAVAN-4-ONES

Abstract The oxidation of the title compounds 1, 4 and 7 with dimethyldioxirane (DMD) afforded the corresponding sulfoxides 2, 5 and 8 and/or sulfones 3, 6 and 9 in good yields (Scheme 1 and 2). Excess dimethyldioxirane gave the sulfones chemoselectively without formation of the epoxides. The epoxidation of the sulfones 6a,b,d to the respective spiroepoxides 10a,b,d required the more reactive methyl(trifluoromethyl)dioxirane (TFD) as oxidant.

DETERMINATION OF THE ABSOLUTE CONFIGURATION OF OPTICALLY ACTIVE 2,2-DIMETHYL-3,4-EPOXYCHROMANS PREPARED BY THE CATALYTIC ENANTIOSELECTIVE EPOXIDATION WITH THE DIMETHYLDIOXIRANE/JACOBSEN MN(III)SALEN SYSTEM

Abstract Enantioselective epoxidation of 2,2-dimethyl-2 H -chromenes 1a-d by using Mn(III)salen complexes (R,R)- 3 and (S,S)- 3 as catalysts and dimethyldioxirane (DMD) as oxygen donor afforded optically active 2,2-dimethyl-3,4-epoxychromans 2a-d in good yields and high enantioselectivities (up to 93% e.e.). The absolute configuration of the (3 S ,4 S )-6,7-bis(tosyloxy)-2,2-dimethyl-3,4-epoxychroman (3S,4S)- 2d has been determined by X-ray diffraction. The absolute configurations of the other nonracemic epoxychromans were assigned by circular dichroism (CD) measurements relative to the (3S,4S)- 2d epoxide as reference compound.

Harvey Cushing, a pioneer of neuroanesthesia

Harvey Cushing’s name is most frequently mentioned in conjunction with Cushing’s syndrome, and Cushing’s reflex following raised intracranial pressure. The aim of this review is to pay tribute to Cushing’s contribution to anesthesia. Besides his own specialty, he used an anesthesia chart for the first time, he introduced blood pressure measurement and precordial auscultation to anesthesiological practice, he employed the first independent neurosurgical anesthetist, and he described the terminology of regional anesthesia.

Stereoselective epoxidation of 2-arylidene-1-indanones and 2-arylidene-1-benzosuberones

SummaryOxidation of the (E) and (Z) isomers of 2-arylidene-1-indanones (1) and 2-arylidene-1-benzosuberones (4) by alkaline hydrogen peroxide (methodi) afforded the spiroepoxidestrans-2a–g andtrans-5a–g from both isomers as sole products in high yields. On the other hand, dimethyldioxirane epoxidation(methodii) of the (E) isomers1a–g and4a–g gave the correspondingtrans spiroepoxides in good yields, whereas the (Z) isomers1a,c,e and4a,c,e led to thecis spiroepoxides in moderate yields. Dimethyldioxirane oxidation (methodii) of (Z)-1c and (Z)-4c,e gave diones3c and6c,e as by-products as well. Epoxidation of (Z)-1a,c,e and (Z)-4a,c,e bym-chloroperoxybenzoic acid (methodiii) resulted inca. 6:1 mixtures ofcis-2a,c,e andtrans-2a,c,e orcis-5a,c,e andtrans-5a,c,e spiroepoxides.ZusammenfassungOxidation der (E)- und (Z)-Isomeren von 2-Aryliden-1-indanonen (1) und 2-Aryliden-1-benzosuberonen (4) mit alkalischem Wasserstoffperoxyd (Methodei) liefert aus beiden Isomeren die Spiroepoxidetrans-2a–g undtrans-5a–g als einzige Produkte. Epoxidierung der (E)-Isomeren1a–g und4a–g mit Dimethyldioxiran (Methodeii) ergab die entsprechendentrans-Spiroepoxide in sehr guten Ausbeuten, während die (Z)-Isomeren1a,c,e und4a,c,e diecis-Spiroepoxide in nur mäßiger Ausbeute liefern. Oxidation von (Z)-1c und (Z)-4c,e mit Dimethyldioxiran (Methodeii) ergab die Dione3c und6c,e sowie einige Nebenprodukte. Wurden (Z)-1a,c,e und (Z)-4a,c,e einer Epoxidation mitm-Chlorperbenzoesäure (Methodeiii) unterworfen, entstanden 6:1-Gemische der Spiroepoxidecis-2a,c,e undtrans-2a,c,e odercis-5a,c,e undtrans-5a,c,e.

Synthesis and stereochemistry of the epoxides of 2-arylmethylidene-1-tetralones

Oxidation of both the E and Z isomers of the 2-arylmethylidene-l-tetralones 1 by alkaline hydrogen peroxide afforded the spiroepoxides trans-2a–g as sole products in high yields. In contrast, the dimethyldioxirane epoxidation of the E isomers la–g gave the corresponding trans spiroepoxides in good yields, while the Z isomers 1a,c,e yielded the respective cis spiroepoxides in moderate yields. Epoxidation of (Z)-1a,c,e by m-chloroperoxybenzoic acid yielded ca. 6 : 1 mixtures of cis-2a,c,e and trans-2a,c,e spiroepoxides. Separation of the isomeric epoxides was achieved by silica gel chromatography and their structures, relative configurations and stereochemistry were elucidated by NMR spectroscopy.

UV-induced isomerisation and ring transformation of (E)-3-arylidene-1-thiochromanones and -1-thioflavanones

Depending on the substituent of the arylidene moiety, photoisomerisation of (E)-3-arylidence-1-thiochroman-4-ones 1 and 3 afforded either the expected (Z)-1 and (Z)-3 isomers or the products (2d,e and 4c,d) of an unprecedented phototransformation.

A VERY MILD AND QUANTITATIVE OXIDATION OF CEPHALOSPORINS WITH DIMETHYLDIOXIRANE

The cephalosporins 1–3 and Δ2-cephem 4 were oxidized in quantative yields to their sulfones with dimethyldioxirane. While in the case of 2-methylene-cephems (5,6) the exocyclic double bond oxidized simultaneously to the corresponding epoxide, the 3-vinyl derivative (8) or 3-methylenecephems (7) gave selectively the corresponding vinyl sulfone.

Structure elucidation of the oxidation products of 2-arylidene-1-indanones and 2-arylidene-1-benzosuberones

The relative configuration and stereochemistry of spiroepoxides prepared by dimethyldioxirane, alkaline hydro‐gen peroxide and m‐chloroperoxybenzoic acid and of dione by‐products were elucidated by various 1H and 13C NMR methods.

Dioxirane oxidation of benzopyrans, benzothiopyrans, and related compounds

Dioxiranes are shown to be powerful and convenient oxidation agents for benzopyrans, benzothiopyrans, and α, β-unsaturated ketones.