Abstract The first example of a N , N ′‐dioxide–Sc III ‐catalyzed 1,6‐addition of 3‐substituted oxindoles to dienyl ketones has been developed. This procedure tolerates a relatively wide range of 3‐substituted oxindoles under mild conditions, facilitating the preparation of various chiral oxindoles with quaternary stereocenters. In addition, the reliable catalyst was found to be effective in the asymmetric 1,6‐addition of both δ‐unsubstituted and δ‐methyl‐substituted dienyl ketones, achieving excellent regioselectivities and enantioselectivities (up to>99 % ee ).
Abstract An N,N′ ‐dioxide/zinc bis(trifluoromethylsulfonyl)imide complex has been developed as an efficient catalyst for the highly enantioselective Diels–Alder reaction of cyclopentadiene with alkynones. Various 2‐acyl substituted norbornadiene derivatives were obtained in moderate to high yields (up to 99 %) with good enantiomeric excesses (up to 95 %). magnified image
Abstract The enantioselective tandem reaction of β,γ‐unsaturated α‐ketoesters with β‐alkynyl ketones was realized by a bimetallic catalytic system of achiral Au ΙΙΙ salt and chiral N , N ′‐dioxide‐Mg ΙΙ complex. The cycloisomerization of β‐alkynyl ketone and asymmetric intermolecular [4+2] cycloaddition with β,γ‐unsaturated α‐ketoesters subsequently occurred, providing an efficient and straightforward access to chiral multifunctional 6,6‐spiroketals in up to 97 % yield, 94 % ee and >19/1 d.r. Besides, a catalytic cycle was proposed based on the results of control experiments.
Abstract Asymmetric cascade double Michael additions to construct 2′‐substituted 3,3′‐spirooxindoles by using a chiral guanidine organocatalyst has been developed. A series of spirooxindole derivatives containing dihydrofuran or pyrrolidine subunits were obtained with good to excellent diastereo‐ and enantioselectivities. The method showed great tolerance of a number of aromatic and aliphatic alkynones. The strategy gave access to the asymmetric synthesis of (−)‐salacin for the first time.
A highly enantioselective conjugate addition/Dieckmann cyclization of 3-carboxymethyl substituted oxindoles with electron-deficient internal alkynes was achieved under the catalysis of a chiral guanidine catalyst and NaH. This protocol provides access to a wide range of synthetically useful optically active spirocyclopentenone oxindoles and their derivatives under mild reaction conditions.
A catalytic asymmetric intra- and intermolecular haloetherification of electron-deficient alkenes (halogen = Cl, Br, I) has been realized by the use of chiral metal complexes of N,N′-dioxides. In the presence of a chiral Fe(III) complex, a series of tetrahydropyran derivatives were obtained in good yields (up to 99% yield) with a high level of enantioselectivities (up to 97% ee). Promoted by a chiral Ce(III) complex, chiral oxepane derivatives could be given in good results. Moreover, the intermolecular haloetherification of chalcones catalyzed by Sc(III) complex using MeOH as nucleophile is demonstrated. This methodology also can be successfully applied to the synthesis of (−)-Centrolobine. Meanwhile, a reasonable reaction mechanism was proposed.
A highly efficient asymmetric imino-ene reaction of cyclic ketimines with silyl enol ethers was developed. Various chiral benzosultam derivatives were obtained in excellent yields (up to 99%), enantioselectivities (up to 99% ee), and diastereoselectivities (up to >19:1 dr) by utilizing a Ni(BF4)2·6H2O/N,N'-dioxide complex as the catalyst. A possible transition state model was proposed to explain the stereoinduction. Furthermore, the synthetic utility of the protocol provided quick access to optically pure HIV-1 inhibitor.
The catalytic enantioselective [1,2]-Wittig rearrangement of allylic ethers is currently unknown. This process constitutes a recognised challenge as it is traditionally considered to arise from a non-concerted reaction pathway via formation and recombination of radical pairs. This manuscript demonstrates a catalytic enantioselective solution to this challenge, and shows that [1,2]-Wittig products are generated via an alternative reaction cascade to traditional dogma. The developed process employs a chiral bifunctional iminophosphorane catalyst to promote an initial enantioselective [2,3]-sigmatropic rearrangement. A subsequent base promoted, stereoconvergent, ionic fragmentation-recombination that proceeds with high enantiospecificity and retention of configuration, formally equivalent to a Woodward-Hoffmann forbidden thermal [1,3]-sigmatropic rearrangement, generates [1,2]-Wittig products in up to 97:3 er. This unique chirality transfer process will have broad implications for fundamental stereocontrol in organic transformations.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='translate(288.889 -214.211)'/%3e%3cuse xlink:href='%23a' transform='translate(108 342.749)'/%3e%3cuse xlink:href='%23a' transform='translate(469.189 342.749)'/%3e%3c/svg%3e)