Catalytic asymmetric access to alpha,beta unsaturated delta-lactones through a vinylogous aldol reaction: application to the total synthesis of the Prelog-Djerassi lactone

Intertwined Analytical, Experimental and Theoretical Studies on the Formation and Structure of a Copper Dienolate

The reaction of a silyl dienolate, a Cu(II) salt and TBAT yielding the corresponding copper dienolate is addressed. A combined NMR and cyclic voltammetry analysis first highlight the role of TBAT in the Cu(II) to Cu(I) reduction and the structure of the precatalytic species. From these first results a second set of NMR and theoretical studies enable the determination of the structure and the mechanism of formation of the copper dienolate catalytic species. Finally, we showed that that the copper catalyst promote the E/Z s-cis/s-trans equilibration of the silyl dienolate precursor through a copper dienolate intermediate. All of these results unveil some peculiarities of the catalytic and asymmetric vinylogous Mukaiyama reaction.

Tandem Insertion/[3,3]-Sigmatropic Rearrangement Involving the Formation of Silyl Ketene Acetals by Insertion of Rhodium Carbenes into S-Si Bonds

Allyl 2-diazo-2-phenylacetates are shown to react with trimethylsilyl thioethers in the presence of rhodium(II) catalysts to generate α-allyl-α-thio silyl esters. The transformation involves a tandem process involving formal rhodium-catalyzed insertion of the carbene group into the S-Si bond to generate a silyl ketene acetal, followed by a spontaneous Ireland-Claisen rearrangement. The silyl ester products were isolated as the corresponding carboxylic acids after aqueous workup. Intramolecular cyclopropanation of the allyl fragment generally competes with addition of the heteroatom to the carbene center. The reaction occurs under mild conditions and in high yield, allowing for rapid entry into rearrangement tetrasubstituted products. Propargyl esters were shown to generate the corresponding α-allenyl products.

Very Recent Advances in Vinylogous Mukaiyama Aldol Reactions and Their Applications to Synthesis

It is a challenging objective in synthetic organic chemistry to create efficient access to biologically active compounds. In particular, one structural element which is frequently incorporated into the framework of complex natural products is a β-hydroxy ketone. In this context, the aldol reaction is the most important transformation to generate this structural element as it not only creates new C-C bonds but also establishes stereogenic centers. In recent years, a large variety of highly selective methodologies of aldol and aldol-type reactions have been put forward. In this regard, the vinylogous Mukaiyama aldol reaction (VMAR) became a pivotal transformation as it allows the synthesis of larger fragments while incorporating 1,5-relationships and generating two new stereocenters and one double bond simultaneously. This review summarizes and updates methodology-oriented and target-oriented research focused on the various aspects of the vinylogous Mukaiyama aldol (VMA) reaction. This manuscript comprehensively condenses the last four years of research, covering the period 2016-2019.

CRM1 inhibitory and antiproliferative activities of novel 4'-alkyl substituted klavuzon derivatives

Klavuzons are 6-(naphthalen-1-yl) substituted 5,6-dihydro-2H-pyran-2-one derivatives showing promising antiproliferative activities in variety of cancer cell lines. In this work, racemic syntheses of nine novel 4'-alkyl substituted klavuzon derivatives were completed in eight steps and anticancer properties of these compounds were evaluated. It is found that size of the substituent has dramatic effect over the potency and selectivity of the cytotoxic activity in cancerous and healthy pancreatic cell lines. The size of the substituent can also effect the CRM1 inhibitory properties of klavuzon derivatives. Strong cytotoxic activity and CRM1 inhibition can be observed only when a small substituent present at 4'-position of naphthalen-1-yl group. However, these substituents makes the molecule more cytotoxic in healthy pancreatic cells rather than cancerous pancreatic cells. Among the tested compounds 1,2,3,4-tetrahydrophenanthren-9-yl substituted lactone was the most cytotoxic compound and its antiproliferative activity was also tested in 3D spheroids generated from HuH-7 cell lines.

Asymmetric Synthesis of Rauhut-Currier type Products by a Regioselective Mukaiyama Reaction under Bifunctional Catalysis

The reactivity and the regioselective functionalization of silyl-diene enol ethers under a bifunctional organocatalyst provokes a dramatic change in the regioselectivity, from the 1,5- to the 1,3-functionalization. This variation makes possible the 1,3-addition of silyl-dienol ethers to nitroalkenes, giving access to the synthesis of tri- and tetrasubstituted double bonds in Rauhut-Currier type products. The process takes place under smooth conditions, nonanionic conditions, and with a high enantiomeric excess. A rational mechanistic pathway is presented based on DFT and mechanistic experiments.

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.

Synthesis of the Prelog-Djerassi lactone via an asymmetric hydroformylation/crotylation tandem sequence

A synthesis of the Prelog-Djerassi lactone [(+)-1] has been accomplished in three isolations and 57% overall yield from the known vinyl ortho ester 2. A Rh(I)-catalyzed asymmetric hydroformylation/crotylation tandem sequence has been developed and used to set the C2-C4 stereochemistry. A Rh(I)-catalyzed asymmetric hydrogenation was employed to set the C6 sterechemistry, resulting in an unusually short and efficient enantioselective synthesis of this touchstone molecule from achiral starting material.

De novo synthesis of natural products via the asymmetric hydration of polyenes

For the last ten years our group has been working toward the development of an asymmetric hydration approach to polyketide natural products based on the regioselective hydration of di- and tri-enoates. Key to the success of this approach is the recognition that both high regiocontrol and asymmetric induction could be obtained by the use of a Sharpless asymmetric dihydroxylation reaction. Herein we describe the development of the method and its application to natural product total synthesis.

De novo synthesis of 2-substituted syn-1,3-diols via an iterative asymmetric hydration strategy

The enantioselective syntheses of several protected 4-substituted syn-3,5-dihydroxy carboxylic esters have been achieved from the corresponding achiral (E,E)- or (E,Z)-1,3-dienoates. The route relies upon an enantio- and regioselective Sharpless dihydroxylation and a palladium-catalyzed reduction to form gamma-substituted delta-hydroxy-1-enoates. The resulting delta-hydroxy-1-enoates are subsequently converted into benzylidene-protected 4-substituted syn-3,5-dihydroxy carboxylic esters in one step. The benzylidene-protected 3,5-dihydroxy carboxylic esters are produced in good overall yields (20-54%) and high enantiomeric excess (73-97% ee).

Asymmetric catalysis for the construction of quaternary carbon centres: nucleophilic addition on ketones and ketimines

There is a growing need in organic synthesis for efficient methodologies for the asymmetric synthesis of quaternary carbon centres. One of the most attractive and straightforward methods focuses on the use of asymmetric catalysis for the addition of various types of nucleophiles on prochiral ketones and ketimines. A view of the literature from this growing area of research will be presented in this review, with an emphasis on the pioneer works and milestones brought by the main players in this field.

α,β-Unsaturated δ-Lactones from Copper-Catalyzed Asymmetric Vinylogous Mukaiyama Reactions of Aldehydes: Scope and Mechanistic Insights

A direct regio-, diastereo-, and enantiocontrolled access to alpha,beta-unsaturated delta-lactones is described, based on the reaction of a silyl dienolate and an aldehyde in the presence of 10 % of Carreira's catalyst. The scope and limitations of this reaction, as well as mechanistic insights concerning the reactivity of an allyl copper species, are discussed.

A rapid divergent synthesis of highly substituted delta-lactones

[reaction: see text] Nucleophilic 1,2-addition of (Z)-gamma-silyloxyvinylzinc reagents to ethyl glyoxylate followed by desilylation and cyclization affords 3,6-dihydro-3-hydroxypyran-2-ones in good chemical yields. In situ formation of allylic phosphates followed by reaction with RCu(CN)Li reagents affords substituted 5,6-dihydropyran-2-ones. The parent compound, 3,6-dihydro-3-hydroxypyran-2-one, undergoes allylic phosphate formation, cuprate-mediated allylic substitution, and 1,4-conjugate addition to afford trans-4,5-disubstituted tetrahydropyran-2-ones in a one-pot process.

Highly Enantio- and Diastereoselective Brassard Type Hetero-Diels−Alder Approach to 5-Methyl-Containing α,β-Unsaturated δ-Lactones

Two efficient new chiral copper (II) Schiff base complexes were developed for the highly enantio- and diastereoselective HDA reaction of Brassard type diene 1b with aldehydes, to afford the corresponding 5-methyl-containing alpha,beta-unsaturated delta-lactone derivatives in moderate yields, high enantioselectivities (up to 99% ee) and excellent diastereoselectivities (up to 99:1 anti/syn). On the basis of the absolute configuration of 4a-4j disclosed by X-ray diffraction and CD analysis, a possible transition-state model for the enantio- and diastereoselective catalytic reaction has been proposed.

Catalytic, Enantioselective, Vinylogous Aldol Reactions

In 1935, R. C. Fuson formulated the principle of vinylogy to explain how the influence of a functional group may be felt at a distant point in the molecule when this position is connected by conjugated double-bond linkages to the group. In polar reactions, this concept allows the extension of the electrophilic or nucleophilic character of a functional group through the pi system of a carbon-carbon double bond. This vinylogous extension has been applied to the aldol reaction by employing "extended" dienol ethers derived from gamma-enolizable alpha,beta-unsaturated carbonyl compounds. Since 1994, several methods for the catalytic, enantioselective, vinylogous aldol reaction have appeared, with which varying degrees of regio- (site), enantio-, and diastereoselectivity can be attained. In this Review, the current scope and limitations of this transformation, as well as its application in natural product synthesis, are discussed.

Catalytic and Asymmetric Vinylogous Mukaiyama Reactions on Aliphatic Ketones: Formal Asymmetric Synthesis of Taurospongin A

Catalytic asymmetric vinylogous Mukaiyama reactions on ketones, leading to the formation of alpha,beta-unsaturated lactones with tertiary alcohols, have been described (11 examples, up to 93% ee). This methodology has been applied in a formal enantioselective synthesis of taurospongin A (12 steps, 6% overall yield).

Lewis Base Activation of Lewis Acids: Catalytic, Enantioselective Addition of Silyl Ketene Acetals to Aldehydes

The concept of Lewis base activation of Lewis acids has been reduced to practice for catalysis of the aldol reaction of silyl ketene acetals and silyl dienol ethers with aldehydes. The weakly acidic species, silicon tetrachloride (SiCl4), can be activated by binding of a strongly Lewis basic chiral phosphoramide, leading to in situ formation of a chiral Lewis acid. This species has proven to be a competent catalyst for the aldol addition of acetate-, propanoate-, and isobutyrate-derived silyl ketene acetals to conjugated and nonconjugated aldehydes. Furthermore, vinylogous aldol reactions of silyl dienol ethers are also demonstrated. The high levels of regio-, anti diastereo-, and enantioselectivity observed in these reactions can be rationalized through consideration of an open transition structure where steric interactions between the silyl cation complex and the approaching nucleophile are dominant.