Marian Keppens

Novel routes to indoles, indolines, quinolines and tetrahydroquinolines from N-(Cyclohexylidene)amines

Abstract Cyclohexanones have been converted into a variety of bicyclic azaheterocycles of different oxidation level via a sequence of reactions involving (a) imination, (b) α-alkylation with N,N-disilyl-protected ω-bromoamines, (c) transimination, (d) α-chlorination of the resulting bicyclic imines and (e) dehydrochlorination and/or dehydrogenation. Appropriate choice of the reaction conditions selectively led the reactions to indoles, 7-chloroindoles, 7-chloroindolines, 4,5,6,7-tetrahydroindoles, 8-chloro-1,2,3,4-tetrahydroquinolines, 8-chloroquinolines or quinolines.

New synthetic route to the alkaloid withasomnine by ring transformation of a functionalized cyclopropanol via the parent pyrrolo[1,2-b]pyrazole

Abstract Withasomnine has been prepared by rearrangement of 1-(3-chloropropyl)-cyclopropanol into 5,6-dihydro-4H-pyrrolo[1,2-b]pyrazole, followed by bromination and [NiCl 2 (dppp)]-catalyzed phenylation.

Cyclocondensations of homophthalic anhydrides with 1-aza-1,3-dienes

Abstract α,β-Unsaturated aldimines (1-aza-1,3-butadienes) 2, 4 and 7a-d react with homophthalic anhydrides 1a,b to give 3,4-dihydro-1(2H)-naphthalenone-4-carboxylic acids 3, 5, 8a-d (R2 = H) as main products. Homophthalic anhydride 1a and cinnamaldimine 7d gave rise to the diastereoisomeric naphthalenones 8d (R2 = H), along with the 3,4-dihydro-1(2H)-isoquinolinone-4-carboxylic acids 10 (R2 = H), and 3,4-dihydro-1(2H)-pyridinone 11 (R2 = H) as products of 3,4-, 1,2- and 1,4-addition to the 1-aza-1,3-butadiene, respectively. The effect of the reaction conditions on the ratio of adducts, produced by 1a and 7d, was studied. The structure and relative configurations of 3, 5, 8a-d, 10 and 11 were determined by NMR spectroscopy. In the case of cis-naphthalenone 8c and dihydropyridinone 11, the structure was confirmed by X-ray crystal structure analysis.

A new approach to symmetric 2,2′:6′,2″-terpyridines

Abstract A novel four step process for the preparation of symmetric terpyridines is presented. The title compound, 2,2′:6′,2″-terpyridine ( 1a ) and a substituted derivative, 5,5″-dimethyl-2,2′:6′,2″-terpyridine ( 1b ) are prepared. Both 1a and 1b share a common precursor, 2,6-diacetylpyridine ( 2 ) and are prepared in overall yields of 73 and 93% respectively. The purities of the crude terpyridine products are in the 90–95% range.

A new efficient synthesis of pyridines

Cyclic six-membered imines, i.e. 2,3,4,5-tetrahydropyridines, are efficiently converted under mild conditions into the corresponding pyridines by highly regioselective α, α-dichlorination with N-chlorosuccinimide (NCS) followed by double dehydrochlorination with methanolic bases.

Synthesis of 2-Aryl-1-pyrrolines from Arylnitriles

Abstract Aromatic nitriles underwent addition of stabase-protected γ-aminopropylmagnesium bromide to afford the corresponding 1-pyrrolines in one step.