Jun Yong Kang

Primary Amine, Thiourea-Based Dual Catalysis Motif for Synthesis of Stereogenic, All-Carbon Quaternary Center-Containing Cycloalkanones

The enantioselective synthesis of α,α-disubstituted cycloalkanones has been developed using a primary amine, thiourea-based dual catalysis pathway. A range of electrophiles and ring sizes are tolerated under the reaction conditions. A possible catalytic cycle is presented to explain the reactivity.

Synthesis of substituted acetylenic epoxides followed by indium-catalyzed rearrangement to 2,3,5-trisubstituted furans.

Syntheses of various aromatic and aliphatic 2,3,5-trisubstituted furans from acetylenic epoxides are described. These epoxides are directly prepared by nucleophilic ring closure of propargylic alkoxides generated by lithium acetylide addition to α-haloketones.

Synthesis of Diaryl Diazaphosphonates via 1,6-Hydrophosphonylation of p-Quinone Methides with N-Heterocyclic Phosphine-Thioureas

A mild, efficient method for the synthesis of diaryl diazaphosphonates via 1,6-hydrophosphonylation/aromatization of p-quinone methides (p-QMs) with N-heterocyclic phosphine-thioureas has been developed. This transformation proceeds without any additive or catalyst under mild reaction conditions and tolerates a wide range of p-QMs. This methodology provides a straightforward access to diaryl phosphonate derivatives in good to excellent yields (up to 99%).

Utility of Bifunctional N-Heterocyclic Phosphine (NHP)-Thioureas for Metal-Free Carbon–Phosphorus Bond Construction toward Regio- and Stereoselective Formation of Vinylphosphonates

An efficient and practical protocol for completely regioselective and highly stereoselective synthesis of vinyldiazaphosphonates from N-heterocyclic phosphine (NHP) and allenes via phospha-Michael/intramolecular nucleophilic substitution reaction has been developed. This transformation enabled the synthesis of valuable densely functionalized vinyldiazaphosphonates with a β-, γ-unsaturated ester moiety under mild reaction conditions. Synthetic utility of vinyldiazaphosphonates was demonstrated by a series of synthetic manipulations.

Chromium-catalyzed homoaldol equivalent reaction employing a nucleophilic propenyl acetate.

A scalable, highly regioselective chromium-catalyzed homoaldol equivalent reaction employing 3-bromopropenyl acetate as a masked homoenolate nucleophile in additions to aromatic, aliphatic, and alpha,beta-unsaturated aldehydes under mild Cr/Mn redox conditions in good to excellent yields is reported. The resulting vinyl acetate-containing adducts are easily hydrolyzed with mild base to provide formal homoaldol adducts, or transformed to other more functionalized products by stereoselective transformations including epoxidation and cyclopropanation.

1,3,2-Diazaphospholidine (N-Heterocyclic Phosphine)-Mediated Carbon–Phosphorus Bond-Forming, One-Pot Tandem Reaction: A Route to α-Amino Phosphonates

A novel 1,3,2-diazaphospholidine (N-heterocyclic phosphine)-thiourea-mediated phospha-Mannich/intramolecular nucleophilic substitution reaction has been developed for the construction of an N-C-P bond unit. This transformation enabled a rapid access to cyclic tertiary α-amino phosphonates in one-pot procedure under additive-free mild reaction conditions. This study revealed the critical role of thiourea moiety of the N-heterocyclic phosphine-thiourea in the sequential intramolecular nucleophilic substitution reaction of the phosphonylation.

Palladium-Catalyzed Alkynylation of Secondary α-Bromo Carbonyl Compounds via Stille Coupling

A catalytic intermolecular cross-coupling reaction that couples secondary α-bromo carbonyl compounds with alkynylstannanes to form secondary alkynyl carbonyl compounds via palladium catalysis employing the XPhos ligand is described.

Catalyst-free synthesis of α1-oxindole-α-hydroxyphosphonates via phospha-aldol reaction of isatins employing N-heterocyclic phosphine (NHP)-thiourea

A highly efficient phospha-aldol reaction for the synthesis of α1-oxindole-α-hydroxyphosphonates is developed utilizing N-heterocyclic phosphine (NHP)-thiourea as a phosphonylation reagent under catalyst, additive free conditions. This methodology encompasses a variety of isatin derivatives to provide α1-oxindole- α-hydroxyphosphonates up to 99% yield.

Phospha-Michael addition reaction of maleimides employing N-heterocyclic phosphine-thiourea as a phosphonylation reagent: synthesis of 1-aryl-2,5-dioxopyrrolidine-3-yl-phosphonate derivatives

N-Heterocyclic phosphine (NHP)-thiourea as a novel phosphonylation reagent has been successfully applied for the phospha-Michael reaction of maleimides under catalyst and additive free reaction conditions. This methodology enables desymmetrization of a variety of maleimide derivatives to provide 1-aryl-2,5-dioxopyrrolidine-3-yl-phosphonates in up to 92% yield. Synthetic manipulation of this Michael adduct afforded an ethylphosphonate and a phosphino lactam. Furthermore, a scale-up experiment for its practical usage as a versatile precursor in organic synthesis was readily demonstrated.

Conversion of nitrosobenzenes to isoxazolidines: an efficient cascade process utilizing reactive nitrone intermediates

Reactive nitrones can be generated directly in situ by an unusual reaction of nitrosobenzene with styrene.