Bor-Cherng Hong

Enantioselective Total Synthesis of (+)-Conicol via Cascade Three-Component Organocatalysis

The first asymmetric total synthesis of (+)-conicol has been achieved via a key step reaction involving the organocatalytic domino oxa-Michael-Michael-Michael-aldol condensation of 2-((E)-2-nitrovinyl)benzene-1,4-diol and alpha,beta-unsaturated aldehydes. Structures of the three-component domino reaction adducts, 20 and 21, including their absolute configurations, were confirmed unambiguously by X-ray analysis. Through this work, the absolute configuration of (+)-conicol was thereby elucidated.

Sequential Organocatalytic Stetter and Michael-Aldol Condensation Reaction: Asymmetric Synthesis of Fully Substituted Cyclopentenes via a [1 + 2 + 2] Annulation Strategy

A stereoselective synthesis of fully substituted cyclopentenes has been achieved by a sequential organocatalyzed Stetter and Michael-aldol condensation of aromatic aldehydes, nitroalkenes, and α,β-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with excellent diastereoselectivities and enantioselectivities (up to >99% ee).

Organocatalytic enantioselective domino Michael-aldol condensation of 5-oxoalkanal and alpha,beta-unsaturated aldehydes. Efficient assembly of densely functionalized cyclohexenes.

Organocatalytic Michael reaction of glutaraldehyde and 3-arylpropenal followed by the subsequent intramolecular aldol condensation provided 2-arylcyclohex-3-ene-1,3-dicarbaldehydes. Reactions with the 5-oxohexanal variant afforded the highly functionalized cyclohexenedicarbaldehydes in high diastereoselectivity and high enantioselectivity (>99% ee). Structure of the adduct 3j was confirmed unambiguously by X-ray analysis.

Dynamic Kinetic Asymmetric Synthesis of Five Contiguous Stereogenic Centers by Sequential Organocatalytic Stetter and Michael−Aldol Reaction: Enantioselective Synthesis of Fully Substituted Cyclopentanols Bearing a Quaternary Stereocenter

A synthesis of fully substituted cyclopentanes bearing a quaternary carbon center and five contiguous stereogenic centers has been achieved by sequential organocatalyzed Stetter and Michael-Aldol reactions of heteroaromatic aldehydes, nitroalkenes, and α,β-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with dynamic kinetic asymmetric transformation and excellent enantioselectivities (up to >99% ee).

Locked ortho- and para-core chromophores of green fluorescent protein; dramatic emission enhancement via structural constraint.

We report the design strategy and synthesis of a structurally locked GFP core chromophore p-LHBDI, its ortho-derivative, o-LHBDI, and H2BDI possessing both para- and ortho-hydroxyl groups such that the inherent rotational motion of the titled compounds has been partially restricted. o-LHBDI possesses a doubly locked configuration, i.e., the seven-membered ring hydrogen bond and five-membered ring C(4-5-10-13-14) cyclization, from which the excited-state intramolecular proton transfer takes place, rendering a record high tautomer emission yield (0.18 in toluene) and the generation of amplified spontaneous emission. Compared with their unlocked counterparts, a substantial increase in the emission yield is also observed for p-LHBDI and H2BDI in anionic forms in water, and accordingly the structure versus luminescence relationship is fully discussed based on their chemistry and spectroscopy aspect. In solid, o-LHBDI exhibits an H-aggregate-like molecular packing, offers narrow-bandwidth emission, and has been successfully applied to fabricate a yellow organic light emitting diodes (λmax = 568 nm, ηext = 1.9%) with an emission full width at half-maximum as narrow as 70 nm.

Enantioselective organocatalytic Michael-Wittig-Michael-Michael reaction: dichotomous construction of pentasubstituted cyclopentanecarbaldehydes and pentasubstituted cyclohexanecarbaldehydes.

Michael addition of carbethoxymethylenetriphenylphosphorane (a Wittig reagent) to nitroalkenes, followed by a reaction with ethyl formylformate and cinnamaldehydes, or formaldehyde and cinnamaldehydes, provided the respective pentasubstituted cyclopentanecarbaldehydes bearing a quaternary carbon center and pentasubstituted cyclohexanecarbaldehydes having five contiguous stereocenters with excellent enantioselectivities (up to >99% ee).

One-Pot Organocatalytic Enantioselective Domino Double-Michael Reaction and Pictet-Spengler–Lactamization Reaction. A Facile Entry to the “Inside Yohimbane” System with Five Contiguous Stereogenic Centers

An expedited method was developed for the enantioselective synthesis of dodecahydrobenz[a]indolo[3,2-h]quinolizine containing five contiguous stereogenic centers with high enantioselectivities (>99% ee). The methodology comprises a domino organocatalytic double Michael reaction and Pictet-Spengler-lactamization reaction. The structures and absolute configurations of the appropriate products were confirmed by X-ray analysis.

Organocatalytic Michael-Knoevenagel-hetero-Diels-Alder reactions: an efficient asymmetric one-pot strategy to isochromene pyrimidinedione derivatives.

Synthesis of isochromene pyrimidinedione derivatives having five stereocenters has been achieved by a one-pot Michael-Knoevenagel condensation-inverse-electron-demand hetero-Diels-Alder reaction of α, β-unsaturated aldehydes, olefinic nitroalkanes, and 1,3-dimethylbarbituric acid via a one-pot strategy with excellent diastereo- and enantioselectivities (up to 99% ee). The structures and absolute configurations of the products were confirmed by X-ray analysis.

Organocatalytic Enantioselective Cascade Michael−Michael−Wittig Reactions of Phosphorus Ylides: One-Pot Synthesis of the all-cis Trisubstituted Cyclohexenecarboxylates via the [1 + 2 + 3] Annulation

The stereoselective synthesis of all-cis 5-nitro-4,6-diphenylcyclohex-1-enecarboxylic ester has been achieved by an organocatalytic asymmetric Michael-Michael-Wittig cascade reaction of phosphorus ylides, nitroolefins, and alpha,beta-unsaturated aldehydes with excellent enantioselectivities (up to >99% ee).

Microwave-assisted [6+ 4]-cycloaddition of fulvenes and α-pyrones to azulene-indoles : Facile syntheses of novel antineoplastic agents

A microwave-enhanced [6+4]-cycloaddition reaction between 6-aminofulvene and pyrones followed by CO(2) extrusion provides azulene-indoles which display interesting antineoplastic activity.