Walter Wever

Multicomponent reactions for the synthesis of heterocycles.

Multicomponent domino reactions (MDRs) serve as a rapid and efficient tool for the synthesis of versatile heterocycles, particularly those containing structural diversity and complexity, by a one-pot operation. These reactions can dramatically reduce the generation of chemical wastes, costs of starting materials, and the use of energy and manpower. Moreover, the reaction period can be substantially shortened. This Review covers recent advances on multicomponent domino reactions for the construction of five-, six-, and seven-membered heterocyclic skeletons and their multicyclic derivatives.

Four-Component Domino Reaction Leading to Multifunctionalized Quinazolines

A new four-component domino reaction has been discovered. The reaction is easy to perform simply by mixing four common reactants and K(2)CO(3) in ethylene glycol under microwave irradiation. The reaction proceeds rapidly and can be finished within 10-24 min with water as the major byproduct, making workup convenient. Four stereogenic centers with one quaternary carbon-amino function are controlled very well; the stereochemistry was unequivocally determined by X-ray structural analysis. The resulting pyrido[3,4-i]quinazoline derivatives are of importance for organic and medicinal research.

New multicomponent domino reactions (MDRs) in water: highly chemo-, regio- and stereoselective synthesis of spiro{[1,3]dioxanopyridine}-4,6-diones and pyrazolo[3,4-b]pyridines

New multicomponent domino reactions (MDRs) have been established for the synthesis of spiro{pyrazolo[1,3]dioxanopyridine}-4,6-diones, spiro{isoxazolo[1,3]dioxanopyridine}-4,6-diones and pyrazolo[3,4-b]pyridines. The MDRs were conducted by reacting readily available and inexpensive starting materials in aqueous solution under microwave irradiation. A total of 26 examples were examined, and showed a broad substrate scope and high overall yields (76–93%). A new mechanism has been proposed to explain the reaction process and the resulting chemo-, regio- and stereoselectivity. The present green synthesis shows attractive characteristics such as the use of water as the reaction medium, one-pot conditions, short reaction periods (9–13 min), easy work-up/purification and reduced waste production without the use of any acids or metal promoters.

Four-Component Domino Reaction Providing an Easy Access to Multifunctionalized Tricyclo[6.2.2.01,6]dodecane Derivatives

A novel four-component domino reaction has been discovered. The reaction is easy to perform simply by mixing four common reactants and Cs(2)CO(3) in ethylene glycol under microwave heating. The reaction proceeds at fast rates and can be finished within 15-24 min, which makes workup convenient. Four stereogenic centers with one quaternary carbon-amino function have been controlled completely. The stereochemistry has been unequivocally determined by X-ray structural analysis. The resulting tricyclo[6.2.2.0(1,6)]dodecane derivatives are of importance for organic and medicinal research.

Asymmetric catalytic Strecker reaction of N-phosphonyl imines with Et2AlCN using amino alcohols and BINOLs as catalysts

The asymmetric catalytic Strecker reaction of achiral N-phosphonyl imines with Et(2)AlCN has been established. Both free amino alcohols and BINOLs have been proven to be effective catalysts to afford excellent enantioselectivities and yields. The N-phosphonyl group can be readily cleaved under mild conditions and enable purification of crude products by simple washing with hexane. The cleaved N,N-dialkyl diamine auxiliary can be recovered quantitatively via n-BuOH extraction. The scope for both N-phosphonyl imines and catalysts was vastly studied for this new catalytic system.

The GAP chemistry for chiral N-phosphonyl imine-based Strecker reaction

Chiral N-phosphonyl imines were found to be efficient electrophiles for reaction with diethylaluminium cyanide, a non-volatile and inexpensive cyanide source. The reaction produced chiral Strecker adducts, α-aminonitriles, in excellent chemical yields (94–98%) and diastereoselectivities (95 : 5 to >99%). This synthesis was confirmed to follow the GAP chemistry (group-assistant-purification chemistry) process, which can avoid traditional chromatography and recrystallization purifications, i.e., the pure chiral α-aminonitriles bearing a chiral N-phosphonyl group can be simply obtained by washing the solid crude products with hexane. The chiral N-phosphonyl auxiliary can be easily cleaved under mildly acidic conditions and quantitatively recycled by a one-time extraction with n-butanol.

Asymmetric hydrophosphylation of chiral N-phosphonyl imines provides an efficient approach to chiral α-amino phosphonates.

Chiral N‐phosphonylimines were found to react with lithium phosphites to provide various substituted chiral α‐amino phosphonates in excellent yields (94–97%) and diastereoselectivities (93:7–99:1). The types of bases utilized for generating the nucleophile are crucial for the effectiveness of asymmetric induction. In addition, N,N‐isopropyl group on chiral N‐phosphonylimine auxilliary was proven to be superior to other protecting groups in controlling diastereoselectivity. The absolute configuration was unambiguously determined by converting a chiral α‐amino phosphonate into its authentic N‐Cbz derivative.

Research Article: Asymmetric Hydrophosphylation of Chiral N-Phosphonyl Imines Provides an Efficient Approach to Chiral α-Amino Phosphonates

Chiral N‐phosphonylimines were found to react with lithium phosphites to provide various substituted chiral α‐amino phosphonates in excellent yields (94–97%) and diastereoselectivities (93:7–99:1). The types of bases utilized for generating the nucleophile are crucial for the effectiveness of asymmetric induction. In addition, N,N‐isopropyl group on chiral N‐phosphonylimine auxilliary was proven to be superior to other protecting groups in controlling diastereoselectivity. The absolute configuration was unambiguously determined by converting a chiral α‐amino phosphonate into its authentic N‐Cbz derivative.

Research Article: Asymmetric Hydrophosphylation of Chiral N-Phosphonyl Imines Provides an Efficient Approach to Chiral α-Amino Phosphonates: Asymmetric Hydrophosphylation of Chiral N-Phosphonyl Imines

Chiral N‐phosphonylimines were found to react with lithium phosphites to provide various substituted chiral α‐amino phosphonates in excellent yields (94–97%) and diastereoselectivities (93:7–99:1). The types of bases utilized for generating the nucleophile are crucial for the effectiveness of asymmetric induction. In addition, N,N‐isopropyl group on chiral N‐phosphonylimine auxilliary was proven to be superior to other protecting groups in controlling diastereoselectivity. The absolute configuration was unambiguously determined by converting a chiral α‐amino phosphonate into its authentic N‐Cbz derivative.