A catalytic asymmetric vinylogous Mukaiyama aldol reaction

Theoretical Design of a Catalyst with Both High Activity and Selectivity in C-H Borylation

Improving both the activity and selectivity of the C-H borylation reaction is currently a hot research topic but also a challenge. In this regard, we suggest a multistrategy combining directing group, coordination unsaturated metal center, and cationic character. Based on Reek's catalyst, we designed a new unsaturated cationic catalyst (1) featuring a directing group for C-H borylation. The calculated free energy barrier of C-H activation is only 7.2 kcal/mol, indicating that the cationic catalyst has higher activity than the original neutral catalyst in this process. Moreover, the comparison suggests that the ortho-C-H borylation pathway is more favorable than the meta and para pathways. The catalyst deconstructions are further performed and prove that the ortho-selectivity is attributed to hydrogen-bonding interactions between the directing group and the substrate, although the ortho site is sterically and electronically unfavorable.

Stereoselective Synthesis of 2,3,5-Trisubstituted Tetrahydrofurans Initiated by a Titanium-BINOLate-Catalyzed Vinylogous Aldol Reaction

The enantioselective synthesis of 2,3,5-trisubstituted tetrahydrofurans 3 has been achieved using a chiral titanium-BINOL complex as catalyst for the vinylogous Mukaiyama aldol reaction of bis(silyl) diendiolate 1 and an aldehyde. The ensuing BF₃·OEt₂-mediated Prins-type cyclization with a second aldehyde gave rise to 2,3,5-substituted tetrahydrofurans 3 with generally good yields and excellent stereocontrol. In this process, three new σ-bonds and three new stereogenic centers were generated in a one-pot process.

Asymmetric Bisvinylogous Aldolation of Aldehydes via 2-Oxonia-Cope Rearrangement Enabling Total Stereochemical Control

Highly stereoselective 2-oxonia-Cope rearrangement reactions between newly designed bisvinylogous aldolation synthons and aldehydes, which can provide ε-hydroxy-α,β,γ,δ-unsaturated esters with excellent enantioselectivities, as well as with unprecedented E- and Z-selectivities without regioselectivity issues, are described.

Rationally Designed Chiral Synthons Enabling Asymmetric Z- and E-Selective Vinylogous Aldol Reactions of Aldehydes

In a conceptually different approach, highly stereoselective 2-oxonia-Cope rearrangement reactions between rationally designed nonracemic vinylogous aldolation synthons and aldehydes are described to provide δ-hydroxy-α,β-unsaturated esters with excellent enantioselectivities and, for the first time, unprecedented Z- and E-selectivities without the regioselectivity issue.

Applications of Keck allylation in the synthesis of natural products

This review highlights the applications of the versatile Keck allylation reaction in the construction of important key fragments of medicinally important natural products.

Chiral N,N′-dioxide–In(OTf)3-catalyzed asymmetric vinylogous Mukaiyama aldol reactions

The chiralN,N′-dioxide–In(OTf)₃catalyst system has been successfully developed to catalyze the vinylogous Mukaiyama aldol reaction of silyl dienol ester with aldehydes. Furthermore, (R,E)-methyl 5-hydroxydec-2-enoate can be easily converted into (R)-δ-decalactone, (3R,5R)-valerolactone and (4R,6R,10R,12R)-verbalactone.

The vinylogous Mukaiyama aldol reaction (VMAR) in natural product synthesis

This review will provide an overview on the recent developments of polyketide synthesis using the vinylogous Mukaiyama aldol reaction for the construction of advanced intermediates. In general, four different motifs can be constructed efficiently using the recent developments of asymmetric variants of this strategy.

Total synthesis and biological assessment of (-)-exiguolide and analogues

We describe herein an enantioselective total synthesis of (-)-exiguolide, the natural enantiomer. The methylene bis(tetrahydropyran) substructure was efficiently synthesized by exploiting olefin cross-metathesis for the assembly of readily available acyclic segments and intramolecular oxa-conjugate cyclization and reductive etherification for the formation of the tetrahydropyran rings. The 20-membered macrocyclic framework was constructed in an efficient manner by means of Julia-Kocienski coupling and Yamaguchi macrolactonization. Finally, the (E,Z,E)-triene side chain was introduced stereoselectively via Suzuki-Miyaura coupling to complete the total synthesis. Assessment of the growth inhibitory activity of synthetic (-)-exiguolide against a panel of human cancer cell lines elucidated for the first time that this natural product is an effective antiproliferative agent against the NCI-H460 human lung large cell carcinoma and the A549 human lung adenocarcinoma cell lines. Moreover, we have investigated structure-activity relationships of (-)-exiguolide, which elucidated that the C5-methoxycarbonylmethylidene group and the length of the side chain are important for the potent activity.

A new method for the synthesis of H(4)-BINOL

A method amenable to the gram scale synthesis of (R)-H 4-BINOL, a derivative of (R)-BINOL and ligand of interest in asymmetric catalysis, is described. The key step is the net partial hydrogenation of (R)-BINOL made possible by prior bis-etherification of the parent BINOL.