Tamas E. Gunda

A new approach for the synthesis of naturally occurring dihydrobenzo[b]furan-type neolignans of potential biological activity

Abstract A new synthesis of racemic naturally occurring neolignan 1 possessing a PGI 2 inducing effect was achieved via the 2,3-dihydrobenzo[ b ]furan derivative 2 , starting from the commercially available materials o -vanillin and acetovanillone.

2-Amino-1-phenyl-propan-1,3-diol as chiral auxiliary. Application in the synthesis of cis 3-Phthalimido-4-styryl-2-azetidinones

Abstract 3,4- cis -1-N-(1′-phenyl-1′,3′-dihydroxy-2′-propyl)-3-phthalimido-4-styrylazetidinones were obtained in optically pure form by chiral Staudinger reaction. The cis -α/β-ratio could be influenced by the protective groups of the diol moiety. Removal of the chiral auxiliarity could be accomplished by direct oxidation, or by previous double bond formation, thus the 2-amino-1-phenyl-propan-1,3-diol can be regarded to a generally useful chiral auxiliary.

A short and facile synthetic route to prenylated flavones. Cyclodehydrogenation of prenylated 2′-hydroxychalcones by a hypervalent iodine reagent

Abstract The first synthesis of the prenylated flavones kanzonol-D (1), -E (3) and yinyanghuo-C (4) was accomplished by cyclodehydrogenation of the appropriately substituted 2′-hydroxychalcones 16, 14 and 11, respectively, in presence of phenyliodine(III) diacetate (PIDA) / potassium hydroxide in methanol. The synthesis of kanzonol-B (13) was also achieved from the 2′-hydroxychalcone 12.

Cycloaddition reactions of carbohydrate derivatives. Part 8: Intramolecular cycloaddition of nitrilimines derived from sugars

Abstract Nitrilimines containing a carboncarbon double bond were prepared in several steps from 2,3,4-tri- O -benzyl- d -xylose, d -ribose and l -arabinose derivatives and their intramolecular 1,3-dipolar cycloaddition reactions were studied. The results were examined with molecular modelling and compared with the literature data for similar cycloadditions.

Asymmetric synthesis of cis 3-phthalimido-4-styryl-2-azetidinones. Application of a new chiral N-protecting group in monobactam chemistry

Abstract 1- N -(1′- p -Nitrophenyl-1′,3′-dihydroxy-2-propyl)-3-phthalimido-4-styrylazetidin-2-ones ( 6a–d ), obtained in optically pure form via chiral Staudinger reactions, were transformed to the N -deprotected derivatives ( 8a,b ) by means of a two-step oxidative procedure.

Reactions of cephalosporin sulphones 2. Rearrangement of 2α-bromocephem sulphones to pyrroles ☆

2α-Bromocephem sulphones exhibit two different rearrangements in acetonitrile solution: first, the tendency for elimination of the bromine as a bromonium ion leads to its formal movement to the para position of the 7β-aromatic ring. Secondly, a bromopyrrole derivative may also form, which can possibly be attributed to an unusual Ramberg-Backlung-like rearrangement followed by bromination.

Stereoselective formation of tricyclic cephalosporins in reactions to cephem phosphorus ylides and ketoaldehydes

Abstract Novel tricyclic cephalosporins ( 3a–d ) and cephem 3-α,β-unsaturated ketones ( 2c–f ) were obtained in a Wittig-type approach with cephalosporin C-3 phosphorus ylides and keto-substituted aldehydes in completely stereoselective reactions. The product ratio was found to be a function of the substituent on the aldehyde. Structure elucidation of the products was carried out by means of NMR methods and molecular mechanics.

REGIOSPECIFIC BROMINATION OF CEPHALOSPORIN SULFONES AT C-2 WITH CYANOGEN BROMIDE

Abstract 2α-Bromocephalosporin sulfones can be prepared very easily and in practically pure form by using commercial cyanogen bromide with base catalysis. The bromides can immediately be used for subsequent reactions.

Mannich Reactions of Cephalosporin Sulphoxides and Sulphones with Imonium Salts. An Improved Synthesis of 2-Methylene-cephalosporins

Abstract 2-Methylenecephem-1-oxides (4) or -1,1-dioxides (6) can be very conveniently obtained through the use of dimethyl(methylene)imonium salts, which can be prepared in situ or in advance from bis(N,N-dimethylamino)methane (2) and a reactive acid derivative.

X-ray structure study of a pyrazolino-cepham (VPNB) C24H23N5O7S

Abstract A tricyclic cepham derivative (VPNB) has been prepared and the relative configuration at the chiral centres C-3, C-4, C-6, C-7 investigated by X-ray analysis.