Enantioselective Diels–Alder reaction of o-quinodimethanes by utilizing tartaric acid ester as a chiral auxiliary

Asymmetric Catalysis of Diels–Alder Reactions with in Situ Generated Heterocyclic ortho-Quinodimethanes

“…7,8 To date, the sporadic examples of enantioselective DielsÀAlder reactions of oQDMs described in the literature require (over)stoichiometric amounts of chiral inducers. 9,10 The challenge of designing a catalytic asymmetric strategy mainly depends on the necessity of generating the highly reactive and unstable oQDMs dienes in situ, in the presence of the trapping reactant (the dienophile). 5,6 Generally, the dearomatization process that leads to these species (intermediate I in Figure 1a) requires harsh reaction conditions and high temperatures, which are not compatible with the action of a chiral catalyst.…”

Magnesium Catalysis in Asymmetric Synthesis

“…Then, the addition of benzocyclobutenols would result in the in situ formation of o-quinodimethanes by deprotonation of the remaining alkylzinc bond; this species could then undergo the [4 + 2] cycloaddition reaction with the Mg(II) Lewis acid-activated fumaric acid ester in the controlled chiral environment, as illustrated in Scheme 54. 106 Furthermore, the same group also utilized Mg(II)/Zn(II) multinuclear systems for the asymmetric alkylation of 3,4-dihydroisoquinoline N-oxides via a similar operational process.…”

Addition Reactions: Cycloaddition

“…91 The enantioselective Diels-Alder reaction of o-quinodimethanes with fumaric acid esters was achieved by utilizing ee diisopropyl (R,R)-tartrate as a chiral auxiliary. 92 DFT studies have been used to investigate the 4 + 2-cycloaddition of ethyl 3,3difluoro-2-(N ,N -diethylcarbamoyloxy)prop-2-enoate with furan and substituted furans in the presence of tin(IV) catalyst. In the presence of SnCl 4 and polar solvents, a twostep reaction was predicted.…”