Synthesis of dihydrobenzazaphosphole ligands via an intramolecular cyclisation reaction

Abstract

A novel intramolecular cyclisation reaction of 1,3,2-oxazaphospholidines has been employed for the diastereoselective synthesis of chiral, non-racemic dihydrobenzazaphosphole ligands. The new ligands have been employed in enantioselective palladium-catalysed allylic substitution reactions. Scheme 3 Reagents and conditions: i) nBuLi, TMEDA, PhPCl 2 , BH 3 ؒSMe 2 Scheme 4 Reagents and conditions: i) nBuLi, TMEDA, PhP(O)Cl 2 , ii) Et 3 N, HSiCl 3 , BH 3 ؒSMe 2 . 1 PERKIN 2588

(2R,4S,5R)-3,4-Dimethyl-5-phenyl-2-[4-(trifluoromethyl)phenyl]-1,3,2-oxazaphospholidine(P—B)borane

“…To our knowledge, no such structure has been reported. Bond lengths and angles within the phosphorus-containing ®ve-membered ring are in accordance with earlier reported oxazaphospholidine borane complexes (Juge et al, 1990;Brunel et al, 1994;Leung et al, 2001).…”

“…Phosphorus-chiral ligands have proven useful for a great variety of asymmetric organic transformations. Ephedrinederived oxazaphospholidines are very interesting precursors for the design and synthesis of novel P-chiral ligands (Juge et al, 1990;Brunel et al, 1994;Leung et al, 2001). P-Chirality moves the stereogenic center close to both the metal and the substrate.…”

On the formation of Pd(II) complexes of Trost modular ligand involving N–H activation or P,O coordination in Pd-catalyzed allylic alkylations

“…When 68 equiv. of 1 were added to a fresh solution of Pd 0 (dba)(4) generated from Pd 0 (dba) 2 (18 mM) and 4 (18 mM) in DMF containing 10% acetone-d 6 , the two doublets of Pd 0 (dba) (4) were not observed on the first recorded 31 P NMR spectrum. The latter exhibited the singlet of the Pd II complex 5 and two kinds of signals which revealed the formation of two different complexes 10 and 11.…”

“…Consequently, the cationic complex 12 + was not formed in significant amount in the oxidative addition, as also confirmed by conductivity measurement (vide supra) due to sluggish ionization steps from the neutral complexes 10 and 11. As a comparison, when the reaction of Pd 0 (dba)(4) with CH 2 @CH-CH-OAc was performed in acetone-d 6 , one singlet was detected in the 31 P NMR spectrum at 31.77 ppm and assigned to the cationic complexes [(g 3 -CH 2 -CH-CH 2 )Pd(4)] + . It is worthwhile to note that under such experimental conditions, no neutral intermediate complex [(g 2 -CH 2 @CH-CH 2 -OAc)Pd 0 (4)] was observed, attesting for its fast ionization.…”

“…Pd 0 (dba) 2 [5] and (E)-1, 3-diphenyl-3-acetoxyprop-1-ene (1) [6] were prepared according to described procedures. [Pd(g 3 -Ph-CH-CH-CH-Ph)(l-Cl)] 2 was synthesized according to a reported procedure [7] but from Na 2 PdCl 4 .…”