The Morita–Baylis–Hillman reaction in aqueous–organic solvent system

Mechanochemistry for Organic and Inorganic Synthesis

In recent years, mechanochemistry has become an innovative and sustainable alternative to traditional solvent-based synthesis. Mechanochemistry rapidly expanded across a wide range of chemistry fields, including diverse organic compounds and active pharmaceutical ingredients, coordination compounds, organometallic complexes, main group frameworks, and technologically relevant materials. This Review aims to highlight recent advancements and accomplishments in mechanochemistry, underscoring its potential as a viable and eco-friendly alternative to conventional solution-based methods in the field of synthetic chemistry.

Discovery and structure-activity relationship of Morita-Baylis-Hillman adducts as larvicides against dengue mosquito vector, Aedes aegypti (Diptera: Culicidae)

Neglected tropical diseases (NTDs) have become a significant public health problem worldwide, notably the life-threatening dengue hemorrhagic fever borne by the Aedes aegypti mosquito. Thus, mosquito vector control measures remain essential in public health vector surveillance and control to combat Aedes-borne infections. Therefore, a series of MBH adducts were synthesized and assessed towards the fourth instar mosquito larvae, Aedes aegypti, along with the preliminary structure-activity relationship (SAR). Noteworthy, this compound class might be synthetized by an efficient eco-friendly synthesismethod and a rapid route for the synthesis of commercial larvicide through a single synthetic step. The bioassays showed that this compound class is a promising larvicide to control Aedes aegypti mosquito larvae, mainly 3g, with an LC₅₀ of 41.35 µg/mL, which was higher than evaluated positive controls. Nevertheless, it is a viable larvicidalhit candidate for further hit-to-leadproperties optimization of its biphenyl backbone scaffold with enhanced insecticidalbioactivity. Moreover, scanning electron microscopy analysis suggested a disruption of the osmoregulatory/ionoregulatory functions by the complete deterioration of the terminal exoskeleton hindgut and anal papillae. Therefore, this new study shows the larvicidal efficacy of the tested compounds against the Aedes aegypti larvae.

Mechanochemical Organocatalysis: Do High Enantioselectivities Contradict What We Might Expect?

Ball mills input energy to samples by pulverising the contents of the jar. Each impact on the sample or wall of the jar results in an instantaneous transmission of energy in the form of a temperature and pressure increase (volume reduction). Conversely, enantioselective organocatalytic reactions proceed through perceived delicate and well-organised transition states. Does there exist a dichotomy in the idea of enantioselective mechanochemical organocatalysis? This Review provides a survey of the literature reporting the combination of organocatalytic reactions with mechanochemical ball milling conditions. Where possible, direct comparisons of stirred in solution, stirred neat and ball milled processes are drawn with a particular focus on control of stereoselectivity.

Morita–Baylis–Hillman reaction in eutectic solvent under aqueous medium

Aqueous solvent-catalyst system formed by DES (1ChCl/2Gly) and DABCO is more useful and practical to the Morita–Baylis–Hillman reaction.

Multivalency as a key factor for high activity of selective supported organocatalysts for the Baylis-Hillman reaction

The polystyrene-supported N-alkylimidazole-based dendritic catalysts for the Baylis-Hillman reaction exhibit one of the strongest beneficial effects of multivalent architecture ever reported for an organocatalyst. The yields in the model reaction of methyl vinyl ketone with p-nitrobenzaldehyde are more than tripled when a non-dendritic catalyst is replaced by a second- or third-generation analogue. Moreover, the reaction of the less active substrates will not occur with the non-dendritic catalyst and will proceed to a significant extent only with the analogous catalysts of higher generations. A substantial additional enhancement of the reaction yield could be achieved by increasing the content of water in the reaction solvent. The plausible cause of the dendritic effect is the assistance of the second, nearby imidazole moiety in the presumably rate-determining proton transfer in the intermediate adduct, after the first imidazole unit induced the formation of the new carbon-carbon bond.

Bio-based solvents for the Baylis–Hillman reaction of HMF

The Baylis–Hillman reaction of HMF was investigated in various bio-based solvent systems and in water.

Aqueous Morita-Baylis-Hillman reaction of unprotected isatins with cyclic enones

The readily available bicyclic imidazolyl alcohol 1 is a unique catalyst for the aqueous Morita-Baylis-Hillman (MBH) reaction between unprotected isatins and cyclic enones that gives access to a variety of potentially very useful 3-substituted 3-hydroxy-2-oxindoles in an operationally simple, efficient, and environmentally friendly way. The hydroxyl group of the catalyst is believed to stabilize the betaine intermediate formed in the first step of the MBH reaction.

An Efficient and Recyclable DMAP-Based Ionic Liquid/Water System for Morita–Baylis–Hillman Reactions

The efficient and recyclable system, DMAP-based ionic liquid/water, has been developed and used in the Morita– Baylis–Hillman reaction of aromatic aldehydes with acrylates. The coupling reactions under the described basic reaction conditions proceed quickly with good to excellent yields. The ionic liquid could be reused at least five times without significant loss of activity.

Remarkable influence of microwave heating on Morita-baylis-Hillman reaction in PEG-200

Background

Morita Baylis Hillman (MBH) reaction is used to introduce carbon-carbon or carbon-heteroatom bond in a molecule. The major drawback of this reaction is the relatively low product yield and long reaction time. Though notable changes have been made to improve the reaction rate and yield of MBH adduct by various groups, a reliable synthetic procedure under ambient temperature in presence moisture and air is remain unsolved. Continuing the effort to improve the rate and yield, we report here an eco-friendly and cost-effective method to generate MBH adducts. Non-volatile polyethylene glycol-200 is used as reusable solvents and the reaction was carried out under the influence of microwave energy.

Results

Microwave irradiation have a remarkable influence on PEG suspended 4-Diazabicyclo [2.2.2] octane (DABCO) catalysed MBH reaction between aldehydes and ethyl acrylate. Molecular weight of the PEG is found to have a significant influence on the reaction yield. PEG-200 was the most efficient solvent and in combination with DABCO, the medium can be recycled upto three more runs. This reaction condition is successfully applied to obtain MBH adduct of five different aldehydes in very short time with excellent yield and the required catalyst concentration was very low compared to standard MBH reaction. Since the MBH adduct is an important reactive intermediates for many complex organic syntheses, this approach can be successfully utilised as an alternative to existing reaction conditions.

Conclusion

A new method was developed to improve the reaction rate and yield of MBH reaction The PEG 200-DABCO combination provides a sustainable, non-volatile, recyclable and environment friendly solvent medium to produce MBH adducts. This medium in combination with microwave energy proved to be very effective to introduce a new carbon-carbon or a carbon-heteroatom bond in a molecule.

Baylis–Hillman reaction under solvent-free conditions — Remarkable rate acceleration and yield enhancement

A simple and efficient method has been developed for remarkable rate acceleration and yield enhancement of the Baylis–Hillman reaction under solvent-free “neat conditions” and solvent-less isolation of products. Reaction of equimolar quantities of aldehyde and olefin in the presence of 20 mol% of DABCO under neat conditions affords the highest yield in most cases within the shortest reaction time, giving support to the mechanisms of proton transfer in protic and aprotic solvents. Solvent-free conditions are found to be especially fast, selective, and high yielding for aromatic aldehydes.

Supported N-alkylimidazole-decorated dendrons as heterogeneous catalysts for the Baylis–Hillman reaction

The activity of supported N-alkylimidazole catalysts could be dramatically enhanced by introduction of a dendritic spacer and further improved by addition of water as a cosolvent.