Arylid-Box: A new family of chiral bis-oxazoline ligands for metal mediated catalytic enantioselective synthesis

Cu(I) catalysed cyclopropanation of olefins: Stereoselectivity studies with Arylid-Box and Isbut-Box ligands

“…recorded (89%) was obtained using ligand 10d with [Cu(CH 3 CN) 4 ]PF 6 in toluene [3], and the best d.e. (40%) using 10e with Cu(II)(OTf) 2 in CH 2 Cl 2 .…”

“…The 1 It must be noted that in our previous two papers [2,3] (R)-(+)-phenylalaninol was inadvertently indicated and as a consequence the configurations of the corresponding amides and Box ligands were wrongly depicted in the relevant schemes. calculation also predicts a stable coordinate bond between N6, N13 and the metal (as the predicted bond orders of 0.475 and 0.463 show).…”

“…These ligands were subsequently used in a series of Cu(I) catalysed olefin cyclopropanations with ethyl diazoacetate [3] using the Cu(I) pre-catalyst, [Cu(CH 3 CN) 4 ]PF 6 and the Cu(II) pre-catalyst, Cu(II)(OTf) 2 (Scheme 3) which was reduced in situ to Cu(I).…”

“…At the outset we expected some correlation between the type of substituted Arylid-Box ligand used and the reaction stereoselectivity, given that both inductive and resonance effects were expected, like for instance, decreased reactivity using para-methoxy substituted Arylid-Boxs 10e and 10f due to the expected reduction in the metallocarbene intermediate electrophilicity. Such trends were not observed [3] and we postulated that this was due to slight tilting of the arylidene phenyl unit out of the plane as suggested by a density functional theory (DFT) study conducted at a B3LYP level [6] that would prevent any significant ressonace effects in such complexes. The DFT study was conducted on the Cu(I)-Arylid-Box 10b complex (for reasons of simplicity, in our model no other ligands were considered nor any counter-ions) by using the GAMESS-US [7] package with the 6-31G * basis-set for C, N, O and H and applying the Stuttgart RSC 1997 [8] effective core potential for Cu (some selected measurements appear in the caption for Fig.…”

“…A second generation series of Boxs with an arylidine bridge between the rings (and termed Arylid-Box) was then developed (Fig. 1) and also tested in a number of benchmark catalytic asymmetric olefin cyclopropanations [3]. In this paper, we wish to report: (1) our full experimental results for the synthesis of our Arylid-Box ligands; (2) our findings on the effect of the counter-ion on the reaction selectivity; (3) our results for comparative studies on the stereoselectivity of the Isbut-Box system with the Arylid-Box system in this reaction (4) studies probing the structure of the catalytic species involved and (5) a comparative DFT study of a particular Arylid-Box-Cu(I) complex with Evans' tert-But-Box-Cu(I) complex and their corresponding metallocarbene complexes.…”