Catalytic Enantioselective Synthesis of 4-Vinyl-2-trichloromethyloxazoline: An Access to Enantioenriched Vinylglycinol Surrogate

Abstract

Cationic Pd(II) catalysts generated from chiral biphenyl diphosphine complexes or from COP-Cl promote enantioselective cyclization of E- and Z-configured allylic bis-trichloroacetimidates to highly enantioenriched 2-trichloromethyl-4-vinyloxazoline. This represents an exclusive example for olefin amination in high yield and enantioselectivity with trichloroacetimidate as the N-nucleophile by using a cationic palladium(II) complex as a catalyst providing an easy-to-deprotect enantioenriched vinylglycinol derivative.

Total Synthesis and Structural Reassignment of Aspergillomarasmine A

“…Our initial attempts began with IBX oxidation of the readily available chiral alcohol 11,w hich was prepared from commercially available 2-butene-1,4-diol in 43 %y ield over four steps, [18] to afford aldehyde 12 in 85 %yield with93 % ee (Scheme 2). [19] Reductive amination of aldehyde 12 with the known amine 13,w hich was obtained from commercially available material in three steps with 65 %y ield and 99 % ee, [20] and subsequent in situ Cbz protection of the newly formed secondary amine moiety smoothly generated diol 14 in 51 %y ield over two steps.O xidative cleavage of diol 14 with NaIO 4 in amixture of THF and H 2 Oprovided the crude aldehyde 15,w hich was used directly in the next reductive amination step involving treatment with either Bn-or t Buprotected aspartic acids 16 and 17,r espectively.U nfortunately,a ll of these attempts failed to deliver the desired product 18.I nstead, during the reductive amination process, we always observed acomplex mixture of byproducts.Based on the preliminary NMR and LC-MS analysis,wepostulated that the major byproduct might be 19,which was presumably generated via dienamine 20 through migration of the terminal double bond under acidic conditions,f ollowed by sequential 1,4-and 1,2-reductions of the iminum species.…”

Chiral Brønsted acid-catalyzed intramolecular SN2′ reaction for enantioselective construction of a quaternary stereogenic center

“…Transition metal complexes as well as achiral Lewis and Brønsted acids have been used as efficient catalysts for this type of transformation. 10 In addition, an enantioselective variant using a chiral palladium catalyst has been reported, 11 although substrate 1 has no substituent (R = H) at the vinyl position, affording the product having a tertiary stereogenic center. It should be emphasized here that the enantio -control of the quaternary stereogenic center has never been reported despite providing a practical access to synthetically useful amino alcohol derivatives 2 (R ≠ H) in an enantio -enriched form.…”

Discussion Addendum for: Preparation of the COP Catalysts: [(S)-COP-OAc]2, [(S)-COP-Cl]2, and (S)-COP-hfacac

“…Jirgensons also reported a COP-catalyzed intramolecular substitution of allylic bis-trichloroacetamidates (Scheme 7). 26 In this case, the E-alkene stereoisomer of the bisimidate was required to achieve high yield and diastereoselectivity.…”