The first Lewis acid mediated asymmetric Torgov cyclisation

The Regioisomeric Triphenylaminoethanols –Comparison of their Efficiency in Enantioselective Catalysis

“…For this purpose, an estrane-based titanium complex had to be used as a chiral Lewis acid. [29] Another problem this protocol Scheme 3. Imines 7, 8 and monochelated titanium complexes 9, 10 derived from the regioisomeric amino alcohols 1 and 2, respectively.…”

“…The enantiomeric excess was determined by comparison of the optical rotation: [a] 20 D : À 39 (c 0.1, tetrahydrofuran); Ref. [29] : [a] 20 D : À 102 (c 0.1, tetrahydrofuran) and by HPLC (Chiracel OJ; Diacel Chemical Industries; n-hexane/2-propanol, 96 : 4): (S)-17: t R 29.3 min; (R)-19: t R 52.4 min The spectroscopic data correspond to these described in the literature [28]…”

Transition-Metal-Catalyzed Reactions in Steroid Synthesis

“…This is in contrast to the enantioselective reactions carried out in the presence of catalysts containing bis-steroidal phosphines of similar structure, where the use of diastereomeric ligands led to enantioselection of a similar magnitude. 158 The same and similar steroidal axially chiral diol ligands induced moderate to high enantioselectivities (up to 82%) in the Ti-catalyzed addition of Et 2 Zn to aldehydes. 252 Chiral C 1 -symmetric phenantrolines incorporated in a steroidal backbone were used as ligands in the enantioselective palladium-catalyzed allylic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethylmalonate.…”

Die katalytische asymmetrische Torgov‐Cyclisierung: eine kurze Totalsynthese von (+)‐Estron

“…[4] Zwar berichteten Wissenschaftler von Schering über Untersuchungen zur Entwicklung einer katalytischen asymmetrischen Version dieser Reaktion, die das Potenzial zur enantioselektiven Synthese von Steroidpharmazeutika bietet, allerdings konnten keine hohen Selektivitäten und Umsatzzahlen erreicht werden. [5,6] Hier berichten wir über eine hochenantioselektive Torgov-Cyclisierung, die von einem neuartigen chiralen Disulfonimid (DSI) katalysiert wird, und dessen Anwendung in der bislang kürzesten Totalsynthese von (+)-Estron [Gl. (1)].…”