Organocatalytic Enantioselective Direct Vinylogous Michael Addition of γ-Substituted Butenolides to 3-Aroyl Acrylates and 1,2-Diaroylethylenes

Asymmetric Phase Transfer Catalysed Michael Addition of γ-Butenolide and N-Boc-Pyrrolidone to 4-Nitro-5-styrylisoxazoles

Herein we report the addition of acidic γ-butenolide and N-Boc-pyrrolidone to 4-nitro-5-styrylisoxazoles, a popular class of cinnamic ester synthetic equivalent. The reactions proceeded under the catalysis of Cinchona-based phase-transfer catalysts. Functionalised γ-butenolides were obtained in good isolated yields and moderate enantioselectivity (up to 74% ee).

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

Deconjugated butenolide: a versatile building block for asymmetric catalysis

Deconjugated butenolides have emerged as a popular synthon for the enantioselective synthesis of γ-lactones. This review provides a comprehensive overview on the catalytic asymmetric reactions of deconjugated butenolides reported till date.

Organocatalytic enantioselective direct vinylogous Michael addition of γ-substituted deconjugate butenolides to azadienes

The diastereoselective and enantioselective direct vinylogous Michael addition of γ-substituted β,γ-unsaturated γ-lactones to 2-arylidene-N-tosylbenzofuran-3(2H)-imines has been achieved with the aid of a quinine-derived squaramide.

A vinylogous Michael addition-triggered quadruple cascade reaction for the enantioselective generation of multiple quaternary stereocenters

An efficient organocatalytic vinylogous Michael addition-triggered quadruple cascade reaction resulting in fused spiroxindoles bearing multiple quaternary stereocenters is demonstrated from β-trifluoroacetylarylidene indanediones and 3-alkylideneoxindoles.

Thiosquaramide-catalysed asymmetric double Michael addition of 2-(3H)-furanones to nitroolefines

2,2,4-Trisubstituted butenolides bearing a quaternary stereogenic center were smoothly constructed with excellent stereoselectivities under mild conditions.

Enantioselective vinylogous Michael addition of β,γ-unsaturated butenolide to 2-iminochromenes

An efficient organocatalyzed asymmetric synthesis of 2-amino-4H-(2-furanone)-3-carbonitrile via vinylogous Michael addition of non-activated β,γ-unsaturated butenolide to 2-iminochromenes has been realized.

Catalytic asymmetric formal γ-allylation of deconjugated butenolides

A formal γ-allylation of deconjugated butenolides is reported based on a two-step sequence consisting of a catalytic diastereo- and enantioselective vinylogous nucleophilic addition to vinyl sulfones and Julia-Kocienski olefination. This highly modular approach delivers densely functionalized butenolides containing a quaternary stereogenic centre in excellent yield with high enantioselectivity.

Angelica Lactones: From Biomass-Derived Platform Chemicals to Value-Added Products

The upgrading of biomass-derived compounds has arisen in recent years as a very promising research field in both academia and industry. In this sense, a lot of new processes and products have been developed, often involving levulinic acid as a starting material or intermediate. In the last few years, though, other scaffolds have been receiving growing attention, especially, angelica lactones. Considering these facts and the emergent applications of said molecules, in this review we will discuss their preparation and applications; the use of these frameworks as starting materials in organic synthesis to produce potential bioactive compounds will be covered, as will their use as a foundation to highly regarded compounds such as liquid alkanes with prospective use as fuels and polymers.

An asymmetric organocatalytic vinylogous Mannich reaction of 3-methyl-5-arylfuran-2(3H)-ones with N-(2-pyridinesulfonyl) imines: enantioselective synthesis of δ-amino γ,γ-disubstituted butenolides

A series of δ-amino γ,γ-disubstituted butenolides were obtained with satisfactory results via an asymmetric vinylogous Mannich reaction of 3-methyl-5-arylfuran-2(3H)-ones with N-(2-pyridinesulfonyl)imines.

Catalytic Asymmetric Synthesis of Butenolides and Butyrolactones

γ-Butenolides, γ-butyrolactones, and derivatives, especially in enantiomerically pure form, constitute the structural core of numerous natural products which display an impressive range of biological activities which are important for the development of novel physiological and therapeutic agents. Furthermore, optically active γ-butenolides and γ-butyrolactones serve also as a prominent class of chiral building blocks for the synthesis of diverse biological active compounds and complex molecules. Taking into account the varying biological activity profiles and wide-ranging structural diversity of the optically active γ-butenolide or γ-butyrolactone structure, the development of asymmetric synthetic strategies for assembling such challenging scaffolds has attracted major attention from synthetic chemists in the past decade. This review offers an overview of the different enantioselective synthesis of γ-butenolides and γ-butyrolactones which employ catalytic amounts of metal complexes or organocatalysts, with emphasis focused on the mechanistic issues that account for the observed stereocontrol of the representative reactions, as well as practical applications and synthetic potentials.

Asymmetric [4 + 2] annulation of 5H-thiazol-4-ones with a chiral dipeptide-based Brønsted base catalyst

Versatile synthetic strategies that access diverse chemical substrates in a highly chemo- and stereo-selective manner are crucial but demanding. Construction of chiral molecules with multiple (hetero)-quaternary carbon stereocenters in a single fashion is a particularly significant challenge, with important applications in the synthesis of a range of bioactive compounds containing the 1,4-sulfur bridged piperidinone structural motif. The asymmetric synthesis of these entities is complicated due to the need to build at least two hetero-quaternary stereocenters concurrently. In order to achieve this, we have developed a new family of dipeptide-based multifunctional Brønsted base organocatalysts that are highly capable of the first asymmetric [4 + 2] annulation reaction of 5H-thiazol-4-ones with electron-deficient alkenes. This protocol could be applied to a series of alkenes such as nitroalkenes, 4-oxo-4-arylbutenones, 4-oxo-4-arylbutenoates and methyleneindolinones, providing an efficient approach to valuable chiral 1,4-sulfur bridged piperidinones and their derivatives with multiple hetereo-quaternary stereogenic centers in high yields and enantioselectivities. Density functional theory studies involving 5H-thiazol-4-one and nitroolefin catalysis propose stereochemical insights into the origin of enantio- and chemo-selectivity.

Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts

Cinchona alkaloids with a free 6'-OH functionality are being increasingly used within asymmetric organocatalysis. This fascinating class of bifunctional catalyst offers a genuine alternative to the more commonly used thiourea systems and because of the different spacing between the functional groups, can control enantioselectivity where other organocatalysts have failed. In the main, this review covers the highlights from the last five years and attempts to show the diversity of reactions that these systems can control. It is hoped that chemists developing asymmetric methodologies will see the value in adding these easily accessible, but underused organocatalysts to their screens.

Diastereodivergent and Enantioselective [4+2] Annulations of γ-Butenolides with Cyclic 1-Azadienes

An asymmetric annulation reaction of γ-butenolides and cyclic 1-azadienes containing a 1,2-benzoisothiazole-1,1-dioxide motif has been studied, proceeding in a tandem Michael addition-aza-Michael addition sequence. Endo-type cycloadducts bearing fused tetracyclic skeletons were isolated in fair yields and with high enantioselectivity (up to >99% ee) under the catalysis of modified cinchona alkaloid (DHQD)₂PHAL. Besides, exo-type diastereomers could be produced using β-isocupreidine (β-ICD) as the catalyst, though with moderate enantioselectivity.

Highly enantioselective direct allylic alkylation of butenolides with Morita–Baylis–Hillman carbonates catalyzed by chiral squaramide-phosphine

Asymmetric vinylogous allylic alkylation of β,γ-butenolides with Morita–Baylis–Hillman carbonates has been developed to construct γ,γ-disubstituted butenolides containing adjacent quaternary and tertiary chiral centers.

Asymmetric vinylogous Michael reaction of cyclic enones with silyloxy furans

A chiral, primary diamine catalyzed enantioselective vinylogous Michael reaction of cyclohexenone/medium and large cyclic enones with various 2-silyloxyfuran has been explored.

Diastereo- and enantioselective direct vinylogous Michael addition of γ-substituted butenolides to 2-enoylpyridines catalyzed by chiral bifunctional amine-squaramides

The enantioselective vinylogous Michael addition of γ-substituted butenolides to 2-enoylpyridines was developed to yield γ,γ-disubstituted butenolide derivatives in excellent stereoselectivities.

An Asymmetric Organocatalytic Quadruple Cascade to Tetraaryl-Substituted 2-Azabicyclo[3.3.0]octadienones

A new asymmetric organocatalytic three-component quadruple cascade of α-ketoamides with α,β-unsaturated aldehydes is described. The reaction is catalyzed by the (S)-diphenylprolinol TMS ether catalyst and proceeds via an aza-Michael/aldol condensation/vinylogous Michael/aldol condensation sequence to yield tetraaryl-substituted 2-azabicyclo[3.3.0]octadienone derivatives. The cascade products are obtained with good to very good yields (34-71%), virtually complete diastereoselectivities (>20:1), and very good enantioselectivities (84-97%).