We report a chiral-squaramide-catalyzed enantio- and diastereoselective synthesis of α-allyl amino esters. The optimized protocol provides access to -carbamoyl-protected amino esters via nucleophilic allylation of readily accessible α-chloro glycinates. A variety of useful α-allyl amino esters were prepared, including crotylated products bearing vicinal stereocenters that are inaccessible through enolate alkylation, with high enantioselectivity (up to 97% ee) and diastereoselectivity (>10:1). The reactions display first-order kinetic dependence on both the α-chloro glycinate and the nucleophile, consistent with rate-limiting C-C bond formation. Computational analysis of the uncatalyzed reaction predicts an energetically inaccessible iminium intermediate, and a lower energy concerted S2 mechanism.
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| http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293823 | PMC |
| http://dx.doi.org/10.1021/jacs.9b05556 | DOI Listing |
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