kn/kr, = 1.65 (50 cal/D).5 In the case of the terminal bromoallene, Id, kH/kD = 1.23 (44 cal/D) for CD3 substitution at C-3 in 70T at 60°. These data strongly support the proposal that terminal haloallenes as well as trisubstituted haloallenes react via charge-delocalized cationic intermediates under initially neutral conditions. The «-secondary isotope effect observed upon deuterium substitution at the reaction center /cH//cD = 1.22 represents one of the largest «-secondary isotope effects yet reported. For saturated chlorides, such as 1-(5) V.

Dedicated to Professor Jack D. Dunitz on the occasion of his 80th birthdayThe diastereoselectivity of the addition of NH 3 and MeNH 2 to glyconolactone oxime sulfonates and the structures of the resulting N-unsubstituted and N-methylated glycosylidene diaziridines wereThe 15 N-labelled glucono-and galactono-1,5-lactone oxime mesylates 1* and 9* add NH 3 mostly axially (> 3 : 1; Scheme 4), while the 15 N-labelled mannono-1,5-lactone oxime sulfonate 19* adds NH 3 mostly equatorially (9 : 1; Scheme 7). The 15 N-labelled mannono-1,4-lactone oxime sulfonate 30* adds NH 3 mostly from the exo side (> 4 :1; Scheme 9). The configuration of the N-methylated pyranosylidene diaziridines 17, 18, 28, and 29 suggests that MeNH 2 adds to 1, 9, 19, and 23 mostly to exclusively from the equatorial direction (> 7 : 3; Schemes 5 and 8). The mannono-1,4-lactone oxime sulfonate 30 adds MeNH 2 mostly from the exo side (85 : 15; Scheme 10), while the ribo analogue 37 adds MeNH 2 mostly from the endo side (4 : 1; Scheme 10). Analysis of the preferred and of the reactive conformers of the tetrahedral intermediates suggests that the addition of the amine to lactone oxime sulfonates is kinetically controlled. The diastereoselectivity of the diaziridine formation is rationalized as the result of the competing influences of intramolecular H-bonding during addition of the amines, steric interactions (addition of MeNH 2 ), and the kinetic anomeric effect.The diaziridines obtained from 2,3,5-tri-O-benzyl-d-ribono-and -d-arabinono-1,4-lactone oxime methanesulfonate (42 and 48; Scheme 11) decomposed readily to mixtures of 1,4-dihydro-1,2,4,5-tetrazines, pentono-1,4-lactones, and pentonamides.The N-unsubstituted gluco-and galactopyranosylidene diaziridines 2, 4, 6, 8, and 10 are mixtures of two trans-substituted isomers (S/R ca. 19 :1, Scheme 2). The main, (S,S)-configured isomers S are stabilised by a weak intramolecular H-bond from the pseudoaxial NH to ROÀC(2). The diaziridines 12, derived from GlcNAc, cannot form such a H-bond; the (R,R)-isomer dominates (R/S 85 : 15; Scheme 3). The 2,3-di-O-benzyld-mannopyranosylidene diaziridines 20 and 22 adopt a 4 C 1 conformation, which does not allow an intramolecular H-bond; they are nearly 1 : 1 mixtures of R and S diastereoisomers, whereas the O H 5 conformation of the 2,3:5,6-di-O-isopropylidene-d-mannopyranosylidene diaziridines 24 is compatible with a weak H-bond from the equatorial NH to OÀC(2); the (R,R)-isomer is favoured (R/S ! 7 : 3; Scheme 6). The mannofuranosylidene diaziridine 31 completely prefers the (R,R)-configuration (Scheme 9).

Die 1,3‐dipolare Cycloaddition des aus den Komponenten (I) und (II) in situ gebildeten Nitrons (IV) an Ethylen (III) liefert bevorzugt das Isoxazolidin (Va), das in den L‐Oxaprolinester (VIa) und nachfolgend in die Derivate (VIb) bis (VId) sowie (VIIa), (VIIb) übergeführt wird.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.