- Expanding the range of "Daniphos"-type P∩P- and P∩N-ligands: Synthesis and structural characterisation of new [(η6-arene)Cr(CO)3] complexes
-
New P∩P- and P∩N-ligands have been synthesised whose core structure is an [(η6-arene)Cr(CO)3] unit. These new ligands, which extend the range of "Daniphos" ligands, are endowed with central and planar chirality and have been prepared through a stereoselective synthetic strategy from optically pure benzylamines bearing a second substituent on the arene other than the benzyldimethylamino group. Because the two faces of unsymmetrically 1,2- and 1,3-disubstituted benzylamine are diastereotopic, which means that diastereomeric complexes arise upon coordination of the Cr(CO) 3 fragment to either of these two faces, the synthetic plan has been adjusted by exploiting the trimethylsilyl group as a temporary steric modulator in order to access both complexes with high diastereoselectivity. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Alberico, Elisabetta,Braun, Wolfgang,Calmuschi-Cula, Beatrice,Englert, Ulli,Salzer, Albrecht,Totev, Daniel
-
p. 4923 - 4945
(2008/09/17)
-
- Base Catalysed Rearrangements involving Ylide Intermediates. Part 15. The Machanism of the Stevens Rearrangement
-
The Stevens rearrangement of acyl-stabilised ammonium ylides has been investigated with regard to stereoselectivity, intramolecularity and the formation of products in addition to the rearrangement product.A detailed study of the effects of reaction conditions upon the rearrangement of the ylide derived from the salt (13) has shown that the stereoselectivity (retention of the configuration of the chiral migrating group) and intramolecularity decrease as solvent viscosity decreases.The rearrangement of the salt (13) in water at 0 deg C is essentially intramolecular with virtually complete retention of the configuration of the migrating group.These results, together with the isolation of products that can be rationalised on the basis of random free-radical coupling, indicate that the rearrangement of acyl-stabilised ammonium ylides normally involves a radical pair mechanism.
- Ollis, W. David,Rey, Max,Sutherland, Ian O.
-
p. 1009 - 1027
(2007/10/02)
-