An asymmetric total synthesis of the Akuammiline alkaloid (−)-vincorine (18 steps from 5-methoxytryptamine, 5% overall yield) is described. The key steps include Pd-catalyzed direct C–H ...functionalization of indole derivatives, organocatalyzed asymmetric Michael addition of aldehydes to alkylidene malonates, and intramolecular oxidative coupling between indole and malonate moieties.
A concise asymmetric total synthesis of (−)-communesin F (∼6% overall yield in the longest linear sequence of 19 steps) is described. It features an unprecedented intramolecular oxidative coupling ...strategy for the elaboration of the requisite spiro-fused indoline moiety. Other notable elements are the use of TBS-protected (S)-phenylglycinol as a chiral auxiliary to induce the asymmetric formation of the spiro-fused indoline part, the mesylate-mediated formation of its G ring, and the introduction of the A ring at the final stage via intramolecular Staudinger reaction. This intramolecular Staudinger reaction proceeded smoothly at 80 °C, providing an additional example illustrating that twisted amides are more reactive than simple amides. Along with the total synthesis, we were able to assign the absolute configuration of natural communesin F as 6R,7R,8R,9S,11R.
A shorter path: A highly enantioselective bromocyclization of tryptamine has been developed using an anionic chiral phase‐transfer catalyst. This method provides a direct approach for preparing ...chiral 3‐bromopyrroloindoline from tryptamine, which enables a four‐step enantioselective synthesis of (−)‐chimonanthine. PG=protecting group.
A highly enantioselective tandem Michael addition of tryptamine‐derived oxindoles to alkynones was developed by taking advantage of a chiral N,N′‐dioxide Sc(OTf)3 catalyst. The reaction enables the ...facile preparation of enantioenriched spiropyrrolidine‐3,3′‐oxindole compounds, which provides a novel strategy for the synthesis of monoterpenoid indole alkaloids. As a demonstration, the asymmetric synthesis of strychnos alkaloids (−)‐tubifoline, (−)‐tubifolidine, (−)‐dehydrotubifoline was achieved in 10–11 steps.
Give me a ring: A novel method for synthesizing strychnos alkaloids was developed in which a chiral N,N′‐dioxide Sc(OTf)3 complex catalyzes the enantioselective tandem Michael addition of tryptamine‐derived oxindoles to alkynones. The reaction enables the facile preparation of enantioenriched spiropyrrolidine‐3,3′‐oxindole compounds, which provides a novel strategy for the synthesis of monoterpenoid indole alkaloids.
Highly asymmetric bromocyclization of tryptophol by using chiral anionic phase-transfer catalyst and DABCO-derived brominating reagent is described. Optimization of the reaction conditions revealed ...that the reaction rate was accelerated together with improvement of enantioselectivity by addition of catalytic DABCO-derived brominating reagent. From tryptophol, 3-bromofuroindoline could be directly obtained in excellent enantioselectivities by employing this novel methodology.
An efficient protocol for assembling a polycyclic spiroindoline scaffold is developed, which involves an intramolecular oxidative coupling of dianions derived from indole-embodied β-ketoamides using ...iodine as the oxidant, and subsequent attack of oxygen anion to the resultant imine moiety. A number of tetracyclic spiroindolines are prepared with moderate to good yields.
By designing a novel chiral ion-pair organocatalyst composed of chiral phosphate and DABCO-derived quaternary ammonium, highly enantioselective 3-
iodo-cycloetherification of allyl alcohols was ...achieved using NIS as a halogen source. Based on this reaction, one-pot asymmetric 3-
iodo-cycloetherification/Wagner-Meerwein rearrangement of allyl alcohols en route to enantioenriched 2-iodomethyl-2-aryl cycloalkanones was subsequently developed. Due to the participation of adjacent iodine, the Wagner-Meerwein rearrangement of 2-iodomethyl-2-aryl epoxide proceeds with unusual retention of stereoconfiguration.
Relying on the nucleophilicity of silanol for building up silicon-incorporated scaffold with an enantiopure tetrasubstituted carbon center remains elusive. In this report, asymmetric ...bromo-oxycyclization of olefinic silanol by using chiral anionic phase-transfer catalyst is described. This protocol provided a facile entry to a wide arrangement of enantiopure benzoxasilole in moderate to excellent enantioselectivities depending on the unique reactivity of bromine/N-benzyl-DABCO complex.
A concise synthesis of polycyclic pyrroloindolines from simple malonic diamides via an intramolecular oxidative coupling/condensative cyclization cascade process is reported. The reaction provides an ...efficient method to construct polycyclic pyrroloindolines in good to excellent yields, which should be useful in the synthesis of natural products and pharmaceutical molecules.
The asymmetric bromohydroxylation of 2‐aryl‐2‐propen‐1‐ols catalyzed by quinine‐derived bifunctional catalyst has been developed. The regioselectivity was controlled by employing a boronate ester as ...tether which was formed in situ and enantioselectivity was introduced by taking advantage of a quinine‐derived bifunctional catalyst which activated the boronate ester and N‐bromosuccinimide (NBS) at the same time. Chiral bromohydrin, which is a useful feedstock in organic synthesis, was produced in moderate to excellent enantioselectivity in a two‐step reaction sequence.
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