On the Synthesis of Isomeric Dithiophene Analogues of Phenathridine- N-oxides

Six of nine o,o\u27-formylnitrobithienyls have been synthesized by the tetrakis(triphenylphosphine)palladium(O)-catalyzed coupling of the three o-bromonitrothiophenes with two of the three o-formylthiopheneboronic acids with sodium carbonate or sodium bicarbonate as base and an ethylene glycol dimethyl ether-water mixture as solvent. In the reaction with 3-formyl-2-thiopheneboronic acid, the coupling was carried out by using triethylamine as base and N,N-dimethylformamide as solvent in an attempt to avoid the facile deboronation of 3-formyl-2-thiopheneboronic acid, but without success. Reduction of the o,o\u27-formylnitrobithienyls gave high yields of the N-oxides of the six isomeric dithienopyridines, which are analogues of phenanthridine-N-oxide. A direct synthesis of one of the dithienopyridines, dithieno[2,3-c:2\u27,3\u27-c]-pyridine, was achieved by the palladium(O)-catalyzed coupling of 2,3-dibromothiophene with 2-formyl-3-thiopheneboranic acid to 3-bromo-2\u27-formyl-2,3\u27- -bithienyl, which was transformed to the 3-azido-2\u27-formyl-2,3\u27- -bithienyl, which upon reduction with hydrogen sulfide underwent ring closure to the phenanthridine analogue

Asymmetric Induction in the Amine-Induced Ring-Opening of 3-Bromo-5-ethyl-2-isopropylthiophene 1,1-Dioxide using L-Prolinol.

Uganda, Wild ElephantsColorVolume 77, Page 1

Asymmetric Induction in the Amine Induced Ring-Opening of 3-Bromo-5-ethyl-2-isopropylthiophene-1,1-dioxide Using L-Prolinol

The diastereomers (1-(2S)-[(2R) (3E,5Z)-5-bromo-7-methyl-3,5-octadien-2-yl]-tetrahydro-1H-pyrrol-2yl) methanol (6) and (1-(2S)-[(2S)(3E,5Z)-5-bromo-7-methyl-3, 5-octadien-2-yl] tetrahydro-1H-pyrrol-2-yl) methanol 7) were formed in a 65:35 ratio from 3-bromo-5-ethyl-2-isopropylthiophene, 1,1-dioxide (5) and L-prolinol. (5R,5aS,8R,9R,9aS,9bS)-Ethyl 7-bromo-8-isopropyl-5-methyl-2,3 ,5,5a,8,9,9a,9b-octahydro-1H-pyrrolo[2,1-a] isoindole-9-carboxylate (10) and (5S,5aS,8R,9R,9aS,9bS)-ethyl 7-bromo-8-isopropyl-5-methyl-2,3,5,5a,8, octahydro-1H-pyrrolo[2,1-a]isoindole-9-carboxylate (12) were synthesized from 6 and 7 in order to establish the absolute configuration of the ring-opened products. The asymmetric induction at C(2) in the ring-opened products can be explained by the preferential formation of E tautomers over Z tautomers and the preferential formation of the E(2S) (15) and Z(2S) (17) enantiomers over the E(2R) (14) and Z(2R) (16) enantiomers when 5 tautomerizes. The tautomers form complexes with the L-prolinol dimers, and the enantiotopic face that will preferentially be attacked by another L-prolinol equivalent in a Michael addition will be the one anti to the dimer and syn to the isopropyl group

Synthesis of Substituted Thiophene-1,1-Dioxides and their Ring-Opening Reactions with w-Unsaturated Secondary Amines; a Synthetic Route to Azatrienes.

The scope and limitations of the ring-opening of thiophene dioxides upon reaction with cyclic secondary amines, leading to dialkylaminomethyl substituted halobutadienes has been further studied. Using ω-unsaturated acyclic secondary amines trienes could be prepared by this methodology

Synthesis of Substituted Benzo[b]indolizidines and Benzo[b]quinolizidines via Ring-Opening of 3-Bromo-2,5-dimethylthiophene-1,1-dioxide

A new method for the preparation of benzo[b]indolizidines and benzo[b]quinolizidines based on two reactions: an amine induced ring-opening of 3-bromo-2,5-dimethylthiophene-1,1-dioxide (1) with 2-allyl-pyrrolidine (2), 2-allylpiperidine (3), 2-[2-(1',3'-dithiolan)methyl]pyrrolidine (4) and 2-[2-(1'-3'-dithiolan)methyl]piperidine (5); and an intramolecular Diels-Alder reaction, is described. Copyright (C) 1996 Elsevier Science Lt