Guillaume Bélanger

Synthesis of the tetracyclic core of daphnilactone B-type and yuzurimine-type alkaloids.

The core of daphnilactone B-type and yuzurimine-type alkaloids was synthesized in only 16 steps from a known β-allyl-γ-butyrolactone. The key sequence of Vilsmeier-Haack cyclization and intramolecular azomethine ylide cycloaddition allowed the construction of, in a single step, three of the five rings common to all alkaloids found in both of these classes with perfect chemocontrol.

Rapid Assembly of Quinolizidines via Consecutive Nucleophilic Cyclizations onto Activated Amides

A new approach to the synthesis of quinolizidines involving a cascade of nucleophilic cyclizations triggered by chemoselective amide activation is reported. Particular attention was given to the effect of the nature of the tethered nucleophiles on the cascade of cyclizations. As a result, simple acyclic amides gave rapid access to functionalized quinolizidines bearing either a tertiary or quaternary center at the ring junction. Such a fused bicyclic motif is found in several alkaloids.

Synthesis of the Tricyclic Core of Alkaloid Securinol B Using a Cascade of Vilsmeier−Haack and Mannich Cyclizations†

Iminium ions generated upon amide activation were trapped sequentially with tethered nucleophiles. This cascade of cyclizations constitutes a new synthetic strategy that was applied to the construction of the tricyclic core of alkaloid securinol B.

A Versatile Cascade of Intramolecular Vilsmeier−Haack and Azomethine Ylide 1,3-Dipolar Cycloaddition toward Tricyclic Cores of Alkaloids†

In the pursuit of synthetic efficiency, we developed an innovative one-pot transformation of linear substrates into bi- and tricyclic adducts using a cascade of amide activation, nucleophilic cyclization, azomethine ylide generation, and subsequent inter- or intramolecular 1,3-dipolar cycloaddition. Despite the high density and variety of functional groups on the substrates, the sequence occurred with perfect chemoselectivity with good to excellent yields.

Asymmetric Total Synthesis of (+)-Virosine A via Sequential Nucleophilic Cyclizations onto an Activated Formamide

The first synthesis of tetracyclic alkaloid virosine A is reported. The natural alkaloid was prepared in only 13 steps, in an enantioenriched form. The azabicyclo[2.2.2]octane core was efficiently assembled using a key Vilsmeier-Haack and Mannich cyclizations sequence performed in one pot.

Highly diastereoselective synthesis of substituted pyrrolidines using a sequence of azomethine ylide cycloaddition and nucleophilic cyclization.

Although cycloadditions of azomethine ylides usually give mixtures of endo/exo adducts, we successfully tuned the mechanistic path of a new reaction cascade to afford substituted pyrrolidines in high yields and diastereomeric purity. This was achieved by forcing the demetalation of tin- or silicon-substituted iminium ions, followed by azomethine ylide cycloaddition and nucleophilic cyclization. Structural complexity is thus built rapidly in a fully controlled one-pot reaction cascade.

Preparation of Conformationally Restricted β2,2- and β2,2,3-Amino Esters and Derivatives Containing an All-Carbon Quaternary Center

β-Amino acids are routinely incorporated into peptidic drugs to increase their stability and to incur conformational biases. However, the synthesis of highly substituted β-amino acids still represents a great challenge. A new approach to their preparation is reported involving a Vilsmeier-Haack reaction with nonaromatic carbon nucleophiles. The highly challenging preparation of contiguous tertiary and all-carbon quaternary centers was successfully used to generate several β(2,2,3)-amino esters, such as derivatives of homoproline, homoalanine, and homopipecolinic esters.

Transannular Diels-Alder studies on the asymmetric synthesis of (+)-maritimol

Abstract Assembly of 13-membered TCC macrocyclic trienes are described and their transannular Diels-Alder reaction are investigated as a model study for the asymmetric synthesis of the ABC-ring system of (+)-maritimol. Albeit the original expectations that the pro-3(S)- and 4(R)-functionalities induce perfect absolute and relative control in the strategic step has not been fully met, a position at pro-12(R) complying with these requirements is recognized.

General Approach toward Aspidospermatan-Type Alkaloids Using One-Pot Vilsmeier–Haack Cyclization and Azomethine Ylide Cycloaddition

The development of a new one-pot reaction sequence afforded the tricyclic core of several aspidospermatan-type alkaloids from a linear, densely functionalized substrate. The key sequence features a highly chemoselective formamide activation that triggered a Vilsmeier-Haack cyclization, followed by an azomethine ylide generation and intramolecular cycloaddition. The choice of nucleophile, azomethine ylide precursor, and dipolarophile was crucial to the success of the sequence.

Short Approach toward the Nonracemic A,B,E Tricyclic Core of Calyciphylline B-Type Alkaloids.

A suitably functionalized tricyclic adduct containing the common A,B,E rings found in calyciphylline B-type alkaloids was obtained in nine linear steps. The key transformation features an efficient one-pot sequence of intramolecular Vilsmeier-Haack cyclization and azomethine ylide 1,3-dipolar cycloaddition in which three cycles, three new carbon-carbon bonds, and three stereocenters are formed, one being fully substituted. This work also demonstrates the first use of a chiral, nonracemic cyclic enol ether as an internal carbon nucleophile.