Stereoselective synthesis of spiro and condensed pyrazolines of steroidal alpha,beta-unsaturated ketones and nitrilimines by 1,3-dipolar cycloaddition.
Effective syntheses of endo- and exocyclic alpha,beta-unsaturated ketones as CC dipolarophiles were carried out in the 13alpha-estrone series. The 1,3-dipolar cycloadditions of 15,16alpha,beta-unsaturated ketones of 13alpha-estrone 3-methyl and 3-benzyl ether with nitrilimines stereoselectively furnished two regioisomers of new condensed pyrazolines in a ratio of 2:1. The main product was the isomer obtained by the attack of the N-terminus of the 1,3-dipole on the carbon atom beta to the carbonyl group of the dipolarophile. The nitrilimine cycloadditions to the 16-methylene-17-ketones of 13alpha-estrone 3-methyl and 3-benzyl ether stereo- and regioselectively furnished spiropyrazolines. The attack of the N-terminus of the dipole occurred on the alpha-carbon of the alpha,beta-unsaturated ketones. The reactions were performed under both homogeneous and heterogeneous conditions. Silver acetate as a base proved more effective than its triethylamine counterpart. Changes in regio- and stereoselectivities were not observed on variation of the conditions of the cycloaddition reactions. The structures of the new products were determined by NMR (one- and two-dimensional) and MALDI TOF MS techniques, with C(70) fullerenes as matrix in the latter case.
Mernyák
Erzsébet
E
Department of Organic Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary. bobe@chem.u-szeged.hu
Kozma
Eszter
E
Hetényi
Anasztázia
A
Márk
László
L
Schneider
Gyula
G
Wölfling
János
J
D003500:Cyclization; D007097:Imines / Q000737:chemistry*; D007659:Ketones / Q000138:chemical synthesis* / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D009570:Nitriles / Q000737:chemistry*; D011720:Pyrazoles / Q000737:chemistry*; D013237:Stereoisomerism; D013256:Steroids / Q000138:chemical synthesis* / Q000737:chemistry
D007097:Imines; D007659:Ketones; D009570:Nitriles; D011720:Pyrazoles; D013256:Steroids