Andreas Rivas Nass

Photochemical Synthesis of Prochiral Dialkyl 3,3-Dialkylcyclopropene-1,2-dicarboxylates with Facial Shielding Substituents and Related Substrates

Different types of cyclopropene-1,2-dicarboxylates 1 have been obtained by photochemical methods from the corresponding pyrazoles 11, 12, or 13. These pyrazoles were synthesized by 1,3-dipolar cycloadditions of alkynes 8 or 9 with either preformed diazoalkanes or diazoalkanes generated photochemically in situ, by use of oxadiazolines as diazoalkane precursors. The numerous substrates have clearly established the scope and limitations of the syntheses of the precursors and the cyclopropenes by the different routes; even prochiral and enantiomerically pure chiral derivatives could be synthesized. Numerous precursors and cyclopropenes could be characterized by X-ray crystal structure analyses, which revealed interesting structural features and allowed unequivocal assignment of different diastereomers or constitutional isomers. Some of the photochemical reactions produced unique side-products; the crystal structure analyses were absolutely crucial for unambiguous structural assignment here.

First and Highly Diastereoselective Synthesis of Palladepanes.

Unexpected stability is observed for the palladacycloheptane rac-2, which is obtained as major product and single diastereomer from the cyclization of 1 and Pd(0). Up to a temperature of 50 degrees C 2 shows neither reductive elimination nor intramolecular insertion of another olefin.

Die erste und hochdiastereoselektive Synthese von Palladepanen

Unerwartetstabil ist das diastereomerenreine Palladacycloheptan rac-2, das als Hauptprodukt einer Cyclisierung von 1 und Pd0 erhalten wurde. Bis zu einer Temperatur von 50 °C erfolgt weder eine reduktive Eliminierung noch die intramolekulare Insertion eines weiteren Olefins in 2.

(Sp)-1-Diphenyl­phosphanyl-2-{(S)-[2-(diphenyl­phosphan­yl)phen­yl]hydroxy­meth­yl}ferrocene

The absolute configuration of the title compound, [Fe(C5H5)(C36H29OP2)], is Sp at the ferrocene group and S at the asymmetric C atom. Both P atoms have a trigonal–pyramidal conformation. There is a short intramolecular C—H⋯P contact with an H⋯P distance of 2.56 Å. The hydroxy group is involved in an intramolecular O—H⋯πphenyl interaction. The crystal packing shows five very weak intermolecular C—H⋯π contacts, with H⋯Cg distances between 3.26 and 3.39 Å (Cg is the centroid of a phenyl or cyclopentadienyl ring).

Low‐temperature phase of di­aqua(1,5‐cyclo­octa­diene)­rhodium(I) tri­fluoro­methane­sulfonate

Crystals of the title compound, [Rh(C8H12)(H2O)2](CF3SO3), undergo a reversible phase transition at 215 (2) K. The high-temperature structure is disordered in space group P21/m with Z′ = ½, while the twinned low-temperature structure is ordered in space group P\overline 1 with Z′ = 2.

(R p)-1-{(R)-(Dimethyl­amino)[2-(diphenyl­phosphan­yl)phen­yl]methyl}-2-(diphenyl­phosphan­yl)ferrocene chloro­form solvate

The absolute configuration of the title molecule, [Fe(C5H5)(C38H34NP2)]·CHCl3, is R,R p. The molecular structure is similar to the structure of the solvent-free compound [Fukuzawa, Yamamoto & Kikuchi (2007 ▶). J. Org. Chem. 72, 1514–1517], but some torsion angles about the P—Cphenyl bonds differ by up to 25°. The P atoms and the N atom have a distorted trigonal-pyramidal geometry. The chloroform solvate group donates a C—H⋯π bond to the central benzene ring and is also involved in six intermolecular C—H⋯Cl contacts with H⋯Cl distances between 2.96 and 3.13 Å.