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Highly Stereoselective Synthesis of Novel Multistereogenic Bis-Bifunctional Ligands Based on [2.2]Paracyclophane- 4,7-quinone, their Structure Elucidation and Application in Asymmetric Catalysis

“…The analysis and comparison of 1 H NMR data of 3 -6 with those obtained for diols 2a -c [4] allowed us to identify the newly synthesized compounds as cis-diols with endo-orientation of the hydroxyl groups. Besides, the structure and the multiplet patterns of signals in the 1 H and 13 C NMR spectra of diols 3 -6 (similar to diols 2a -c) indicate the formation of compounds of C 2 -symmetry in all cases.…”

“…To rationalize the formation of such a product we assume that the addition of the organolithium reagent to one carbonyl group of quinone 1 occurs stereospecifically from the outer site of the carbonyl group, like the double addition to this substrate. [4] The ensuing coordination between lithium and the nitrogen atom of the proximate NEt 2 group provides the generation of the rigid intermediate 7* which suffers the elimination of the lithium diethylamide. Further cyclization produces lactone 7 which forms, as a matter-of-course, stereospecifically and has the (Rp*,Rc*)-relative configuration (Scheme 2).…”

“…The exclusive formation of the mono-addition product could be explained if one assumes that the second carbonyl group of the paracyclophane scaffold (either in the intermediate 7* or in the final product 7) is shielded by the aromatic ring of paracyclophane moiety from one side, and by the aromatic ring of the substituent from the other, thus preventing the approach of the organolithium reagent to this group. The application of the regularities of nucleophilic addition of ortho-functionalized aryllithium reagents to enantiomers of quinone 1 [3,4] allowed us to synthesize compounds 3 -5, in which the aryl substituents have in the ortho-positions various groups (N-or O-functions), in optically active form. The pairwise combination of these functional groups of the aryl fragments together with the geminal hydroxy groups provides the formation of two independent (concomitantly chemically and stereochemically identical) systems, both of which are capable of chelation with metals in the course of asymmetric synthesis and catalysis.…”

“…In our previous papers we have described chemical transformations of quinone 1 and its derivatives. [3,4] In particular, we have shown that the nucleophilic addition of alkyl-and aryllithium reagents to rac-quinone 1 occurs regio-and stereospecifically (from the outer site of both carbonyl groups), resulting in the corresponding multistereogenic diols (Rp*,4Rc*,7Rc*)-2a -c (Figure 1). [4] However, two hydroxy groups of diols 2a -c have the endo-orientation and are, for this reason, not capable of chelation with metals.…”

“…[3,4] In particular, we have shown that the nucleophilic addition of alkyl-and aryllithium reagents to rac-quinone 1 occurs regio-and stereospecifically (from the outer site of both carbonyl groups), resulting in the corresponding multistereogenic diols (Rp*,4Rc*,7Rc*)-2a -c (Figure 1). [4] However, two hydroxy groups of diols 2a -c have the endo-orientation and are, for this reason, not capable of chelation with metals. Therefore, we have envisaged constructing a novel series of ligands of type A (Figure 1) containing ortho-functionalized aryl moieties as R. In such ligands hydroxy groups bound to the [2.2]paracyclophane scaffold pairwise with functional groups of the aryl fragments will form two independent systems, both of which are capable of coordination with metals and so could work as chiral promoters.…”