Heinz Braun

Asymmetric diels - alder reacrions with α-chloronitroso compounds- II. The use of a carbohydrate derived α-chloro-α-nitroso ether

Abstract The Diels-Alder reaction of 1,3-cyclohexadiene with the α-chloro-α-nitroso ether 2, prepared from mannose via the lactone oxime 1, gives the adduct 3 with 1-(S),4-(R) configuration in 69 % chemical yield and ⩾ 95 % enantiomeric excess.

Asymmetric Diels-Alder reactions with α-chloronitroso compounds. I: Application of α-chloronitroso epiandrosterone in synthesis

Abstract The Diels - Alder reaction of 1,3-cyclohexadiene (9) with the enantiomerically pure α-chloronitroso compound 8, synthesized from epiandrosterone (7a), gives the adduct 10a with 1-(R),4-(S) configuration in 69 % chemical yield and ⩾95 % enantiomeric excess.

Synthese und Reaktionen von Enaminosulfoniumsalzen / Syntheses and Reactions of Enaminosulfonium Salts

A general method for preparing (E)-alkylamino and dialkylamino vinylsulfonium salts is reported. The hydrolysis and some alkylation and acylation reactions have been examined. The 2,2-dihydroxyethyl sulfonium salt (9 a) is produced by acid hydrolysis of 4 a. In the reaction of 4h with trimethyloxonium salt and acyl halides the N-alkylated and N-acylated products 4 a and 11 are formed respectively. (E)-N,N-diacylated compounds (12) are obtained from 41 and 51 by the reaction with excess acyl halides. On treatment with base, 11a forms mixtures of the (E)- and (Z)-sulfonium imido ylides 14 and 15.

Dynamisches Verhalten, Konformation und Bindungsverhältnisse von Enaminosulfoniumsalzen / Dynamic Behaviour, Conformation and Bonding of Enaminosulfonium Salts

Abstract The rotational barriers about the C-N single bond of the enaminosulfonium salts 1-6 are measured. Their magnitudes are related to the π-donor strength of the NR2 group. For the unsymmetrically substituted compounds 7-12 the rotational equilibria are determined. In the case of the monoalkyl compounds 7-10 the more crowded s-cis-rotamers turn out to be the more stable conformations. Furthermore, the 13C chemical shifts of the sulfonium salts 1-16 are reported. The shift differences δ(s-cis-s-trans) for the α-carbons of the N-alkyl groups seem to depend on the dihedral angle between the vinyl group and the C-H(α-c) bonds. Moreover, the spectra reveal that enaminosulfonium salts posses a high degree of ylide character.