Efficient Baylis--Hillman reaction using stoichiometric base catalyst and an aqueous medium

Acceleration of the Morita-Baylis-Hillman reaction by a simple mixed catalyst system

By using a catalytic amount of 4-dimethylaminopyridine (DMAP) as a nucleophile in the presence of an equal amount of tetramethylethylenediamine (TMEDA) and MgI(2), Morita-Baylis-Hillman adducts can be obtained in good to excellent yields from various aromatic and aliphatic aldehydes and cyclic enones/enoates at room temperature after convenient reaction times.

Theory-Guided Design of Brønsted Acid-Assisted Phosphine Catalysis: Synthesis of Dihydropyrones from Aldehydes and Allenoates

The phosphine-catalyzed addition of 2,3-butadienoates to aldehydes has been extended to the formation of disubstituted dihydro-2-pyrones. The requisite shift in equilibrium of the intermediate zwitterionic beta-phosphonium dienolates toward the s-cis intermediate was accomplished through the use of a Brønsted acid additive, which disrupts the favorable Coulombic interaction present in the s-trans intermediate. The detailed nature of the synergistic interactions involving the Brønsted acid additives and phosphine involved in the formation of s-cis beta-phosphonium dienolates was analyzed through a series of DFT calculations. Unlike previously reported annulations of aldehydes with allenoates, where trialkylphosphines are optimal catalysts, in this study triphenylphosphine was also found for the first time to be a suitable catalyst for the synthesis of dihydropyrones. This method provides a one-step route toward functionalized dihydropyrones from simple, stable starting materials. In addition, new reaction pathways of phosphine-catalyzed allene annulations are unveiled, with the formation of dihydropyrones being the first example of dual activation in this sphere.

Ab initio and density functional theory evidence on the rate-limiting step in the Morita-Baylis-Hillman reaction

The first ab initio and DFT studies on the mechanism of the MBH reaction show that the rate-limiting step involves an intramolecular proton transfer in the zwitterionic intermediate generated by the addition of enolate to electrophile. The activation barrier for the C-C bond-formation is found to be 20.2 kcal/mol lower than the proton-transfer step for the MBH reaction between methyl vinyl ketone and benzaldehyde catalyzed by DABCO.

The enantioselective Morita-Baylis-Hillman reaction and its aza counterpart

The development of asymmetric Morita-Baylis-Hillman (MBH) reactions has evolved dramatically over the past few years, parallel to the emerging concept of bifunctional organocatalysis. Whereas organocatalysis is starting to compete with metal-based catalysis in several important organic transformations, the MBH reaction belongs to a group of prototypical reactions in which organocatalysts already display superiority over their metal-based counterparts. This Minireview summarizes recent mechanistic insights and advances in the design and synthesis of small organic molecules for enantioselective MBH and aza-MBH reactions.

Asymmetric Synthesis of 2-Alkyl-3-phosphonopropanoic Acids via P−C Bond Formation and Hydrogenation

Allylic acetates, formed by the acetylation of Baylis Hillman adducts, undergo addition of phosphorus nucleophiles to give stereoselectively the Z-unsaturated esters. TFA cleavage of the tert-butyl ester and asymmetric hydrogenation of the unsaturated acid yields the phosphono alkyl propanoic acid moiety, commonly found in phosphonate- and phosphinate-based enzyme inhibitors.

Nonenzymatic Acylative Kinetic Resolution of Baylis−Hillman Adducts

The first efficient nonenzymatic acylative kinetic resolution of Baylis-Hillman adducts is reported. Chiral pyridine catalyst 1a and an optimized analogue 1e are capable of promoting the synthetically useful enantioselective acylation (the efficiency of which is outstanding for sp(2)-sp(2) carbinol substrates, s = 3.5-13.1, ee up to 97%) of Baylis-Hillman adducts derived from recalcitrant precursors which are currently difficult to synthesize utilizing benchmark asymmetric Baylis-Hillman reaction catalyst technology. A novel one-pot synthesis-kinetic resolution process involving a DBU-catalyzed Baylis-Hillman reaction and subsequent 1e/DBU-mediated enantioselective acylation has also been developed.

Dual Reactivity Pattern of Allenolates “On Water”: The Chemical Basis for Efficient Allenolate-Driven Organocatalytic Systems

A study of the reactivity pattern associated with zwitterionic allenolates "on water" is reported. This study establishes the chemical basis for two organocatalyzed allenolate-driven reaction networks operating "on water". The first one is a chemodifferentiating three building block (ABB') three-component reaction (ABB' 3CR) manifold comprising terminal alkynoates and aldehydes. The manifold produces propargylic enol ethers 3 with higher average efficiency than their homologues in organic solvents. The second one is a novel organocatalytic system elicited by the reaction of alkynoates and nitrones in the presence of tertiary amines or phosphines. While terminal alkynoates afford 2,3,5-trisubstituted 2,3-dihydroisoxazoles 5 and propargylic N-hydroxylamines 6, internal alkynoates selectively afford the 2,3,4,5-tetrasusbstituted 2,3-dihydroisoxazaole 10. Importantly, in both cases, the 2,3-dihydroisoxazole ring is obtained as a sole regioisomer.

Bifunctional Polymeric Organocatalysts and Their Application in the Cooperative Catalysis of Morita–Baylis–Hillman Reactions

A series of soluble, non-cross-linked polystyrene-supported triphenylphosphane and 4-dimethylaminopyridine reagents were prepared. Some of these polymeric reagents contained either alkyl alcohol or phenol groups on the polymer backbone. The use of these materials as organocatalysts in a range of Morita-Baylis-Hillman reactions indicated that hydroxyl groups could participate in the reactions and accelerate product formation. In the cases examined, phenol groups were more effective than alkyl alcohol groups for catalyzing the reactions. This article is one of the first reports of the synthesis and use of non-natural, bifunctional polymeric reagents for use in organic synthesis in which both functional groups can cooperatively participate in the catalysis of reactions.

An Efficient Synthesis of 2-Benzoxepines from Morita-Baylis-Hillman Adducts Using Heterogeneous Recyclable Catalysts

2-Benzoxepines have efficiently been synthesized from Morita-Baylis-Hillman adducts, alkyl 3-aryl-3-hydroxy-2-methylenepropanoates by treatment with HCHO catalyzed by silica supported perchloric acid (HClO4.SiO2) or Amberlyst-15 in CH2Cl2 under reflux for a short period of time (1.5-2.5 h). The catalyst can be recovered and recycled. The antibacterial properties of the new 2-benzoxepines were studied but no activity was found.

Acrylamide in the Baylis-Hillman reaction: expanded reaction scope and the unexpected superiority of DABCO over more basic tertiary amine catalysts

DMAP, DBU, and quinuclidine efficiently promote novel hydroalkoxylation reactions of acrylamide in primary alcohol solvents. DABCO is a comparatively poor hydroalkoxylation promoter and can effect clean, selective Baylis-Hillman reactions between acrylamide and aldehydes in alcoholic/aqueous media in which more basic nucleophilic catalysts promote hydroalkoxylation preferentially. Optimization of the reaction conditions has allowed acrylamide to be reacted with a range of aromatic aldehydes in moderate to excellent yields, including the first examples involving deactivated, electron-rich substrates such as p-tolualdehyde and o-anisaldehyde.