Ultrasound-promoted selective formation of optically active cyclopentadienyl ligands

Optically active cyclopentadienyl and indenyl ligands obtained from lactic acid esters

“…1 H NMR (CDCl 3 , 200 MHz): d 7.51-7.19 (m, 4H, CH arom), 6.32 (m, 1H, CH indene), 3.81 (m, 2H, CH 2 OH), 3.37 (bs, 2H, CH 2 indene), 3.11 (qd, 1H, CHCH 3 ), 1.48 (bs, 1H, OH), 1.33 (d, 6.9, 3H, CH 2 CH 3 ). 13 A solution of racemic 2 (0.3 g, 1.8 mmol) in 15 ml toluene cooled at À10°C was slowly added to 0.485 g (1.8 mmol) of Zr(NMe 2 ) 4 in 15 ml toluene kept at À10°C.…”

“…The resulting red solution was stirred at room temperature during 24 h. Elimination of Zr(NMe 2 ) 3 (OEt) by filtration at À20°C, followed by chromatography of the filtrate on silica gel, afforded 12 as an oily yellow liquid (0.26 g, 87.5% yield). 1 Crystallization from hexane/Et 2 O afforded yellow crystals suitable for X-ray analysis.…”

“…From methyl(À)-pinane-3-carboxylate [1,5], using the Bercaw's method [6], we could obtain optically active cyclopentadienes (Scheme 1). This method was also successfully applied to (S)-(+)-naproxene and 2-bromo-butene [7] (Scheme 2).…”

“…As part of our interest in the synthesis of optically active cyclopentadienyl ligands, we have recently reported the preparation of differently substituted chiral cyclopentadienes and indenes [1][2][3][4] from various natural products.…”

Influence of the stereochemistry of sugars on the selectivity of formation of carbohydrate-derived cyclopentadienyl and indenyl ligands

“…The synthesis of optically active transition metal complexes is an important area of research for asymmetric catalysis, and chiral ligands such as cyclopentadienyl and indenyl carbohydratederivatives are of interest. 1 Cyclopentadienes and indenes have recently been derived from different natural products such as sugars, 2 disaccharides and nucleosides 3 as well as esters 4 and hydroxyesters. 5 Suitably protected a-D-glucofuranose or a-Dgalactopyranose derivatives that contain one active -OH group as a triflate ester function react with cyclopentadienide or indenide anions to produce the corresponding substituted cyclopentadienes and indenes in good to moderate yields.…”