Hen CuI(OTf)benzene complex/(S)MefKetalPhos (14)/Et3N method is employed, the enantioselectivity of cycloaddition of azlactone 1d, endowed having a far more hindered benzyl group, onto [60]fullerene is still higher with 88 of ee (entry four, Table 3). The complicated silver(R,R)BPE (12) gave rise to slightly reduce enantioselectivity (68 ). Interestingly, its chiral induction sense resulted substrate dependent, and it reverted when the phenylalaninesubstituted azlactone 1d was employed (entry four, Table three). Therefore, such cycloaddition afforded the opposite enantiomer of pyrroline 2d. Azlactones depending on glycine, 1e,f, showed moderate conversions possibly as a consequence of a less stability from the final products (also the trapping from the additional acidic second proton affords side solutions and/or racemization processes). Additionally, the pair CuI(OTf)benzene complex/(R)FeSulPhos (13) leads generally to the (R)two goods. Within the case of pyrrolinofullerene 2g, this copper technique with (R)FeSulPhos (13) performed even greater with regards to ee than (S)MefKetalPhos (14), 96 (R2g) vs 90 (S2g), respectively (entry 7, Table 3). As a result, copper chiral systems allow the efficient switching on the enantioselectivity of your formed pyrrolino[3,4:1,2][60]fullerenes and with improved conversion and ee values than the silver chiral technique. Ultimately, distinct substitution on the aryl ring from the oxazolone with donating or electronwithdrawing groups did not modify the behavior of these substrates. Therefore, items 2hj had been obtained with excellent ee values (8294 ) when CuI(OTf)benzene complex/(S)MefKetalPhos (14)/Et3N method was employed (entries 810, Table 3). Alternatively, organocatalysis also gives superior to exceptional conversion and enantiomeric excesses. Nonetheless, improved benefits on enantioselectivity had been obtained for significantly less hindereddx.doi.org/10.1021/ja500071k | J. Am. Chem. Soc.120042-11-7 Formula 2014, 136, 2897Journal with the American Chemical Society Table 3. Scope of your Enantioselective 1,3Dipolar Cycloaddition of Azlactones 1aj with [60]FullereneArticledx.doi.org/10.1021/ja500071k | J. Am. Chem. Soc. 2014, 136, 2897Journal of your American Chemical Society Table 3. continuedArticleGeneral reaction situations: A mixture of the triazolium salt (1 equiv), [60]fullerene (1 equiv), as well as the base (ten equiv) in 1 mL of solvent is stirred for 10 min at rt, then 0.016 mmol of azlactone 1aj (two equiv) is added. Right after 30 min reaction, excess of DCC is added.3-Methoxybenzensulfonyl chloride custom synthesis bGeneral reaction situations: A mixture of 0.PMID:24914310 01 mmol azlactone 1aj, [60]fullerene (1 equiv), metal salt (20 mol ), ligand (20 mol ), and Et3N (1 equiv) in 1.five mL of chlorobenzene is stirred for 1 h at 0 , then excess of DCC is added. cConversion and ee have been determined by HPLC analysis. Isolated yields have only been determined for the racemic mixture (see SI). As a basic trend, larger conversions correspond to greater yields. dAbsolute configuration has been assigned on the base of CD measurements. eCuI(OTf)benzene complicated.aoxazolones including 1a, 1h, or 1j, in which also an efficient switching on the enantioselectivity is accomplished depending on the triazolium saltNHC utilised (8488 ee with 8a and 7484 ee with 8b; entries 1, eight and 10, Table 3). Regrettably, this methodology appears to become significantly extra substrate dependent than the metallic one particular (see, for example, entries 4 or 7, Table three). All in all, milder reaction conditions and larger conversion values make the organocatalytic methodology an efficient tool for the synthesis of this sort of fullerene derivatives in larg.
