Biomedical subjects

Daesung Lee

Publications and source records attributed to Daesung Lee.

26 records · Page 2Linked to original sources

PubMed2004

Regio- and stereoselective enyne cross metathesis of silylated internal alkynes.

Cross metathesis between silylalkynes and various functionalized alkenes catalyzed by Grubbs carbene complex produced, in most cases, single regio- and stereoisomers of the resultant 1,3-dienes. Polar heteroatom substituents at the propargylic site are important for high reactivity and selectivity. An important mechanistic insight regarding the initiation event and the key propagating alkylidene in this reaction was obtained by employing a tandem cross metathesis ring-closing metathesis between a terminal alkene and a silylated alkyne possessing an alkene tether.

Alkenes↗

PubMed2004

Ruthenium-catalyzed silyl ether formation and enyne metathesis sequence: synthesis of siloxacycles from terminal alkenyl alcohols and alkynylsilanes.

Two consecutive ruthenium-catalyzed reactions have been achieved for the synthesis of siloxacycles from terminal alkenyl carbenols and alkynylsilanes. The metal-catalyzed dehydrogenative condensation between alcohols and silanes, generating molecular hydrogen as the only byproduct, allows for the subsequent enyne metathesis without isolating the intermediate silyl ethers. This system provides a streamlined synthesis of synthetically useful building blocks. [reaction: see text]

Alcohols↗

PubMed2004

Efficient and Z-selective cross-metathesis of conjugated enynes.

[reaction: see text] The generation of a conjugated alkynyl alkylidene has been achieved using an allyl ether moiety as an intramolecular catalyst delivery vehicle. The reaction of this intermediate with alkenes and alkynes yields conjugated enynes with Z-selectivity.

Alkenes↗

PubMed2004

Transition-metal-catalyzed aldehydic C-H activation by azodicarboxylates.

Rhodium acetate-catalyzed hydroacylation between aldehydes and an activated form of N=N bond was achieved under mild conditions to provide efficient access to a variety of hydrazino imides. Good selectivity for the aldehydic C-H activation relative to the ene-type reaction was observed with aldehydes having unsaturation both at terminal and internal positions.

Journal Article↗

PubMed2003

Stereochemical control of skeletal diversity.

[reaction: see text]. Substrates having appendages that pre-encode skeletal information (sigma-elements) can be converted into products having distinct skeletons using a common set of reaction conditions. The sequential use of the Ugi 4CC-IMDA reaction, followed by allylation, hydrolysis, and acylation of a chiral amino alcohol appendage (sigma-element), leads to substrates for a ROM/RCM or RCM reaction. The stereochemistry of the sigma-element and not its constitution controls the outcome of the pathway selected. This work illustrates the potential of linking stereochemical control to the challenging problem of skeletal diversity.

Catalysis↗

PubMed2003

Enyne metathesis for the formation of macrocyclic 1,3-dienes.

Macrocyclic 1,3-dienes of a variety of ring sizes are formed in good yield via enyne metathesis. Both endo- and exo-products are observed depending on the size of the macrocycle. In general, 10-membered rings and smaller give exo-products, while 12-membered rings and larger give endo-products. The endo/exo selectivity and the E/Z ratio of the diene products can be further controlled by the presence of ethylene in the reaction.

Alkynes↗

PubMed2002

Synthesis of the 5-7-6 core of guanacastepenes. Construction of C8 quaternary carbon via the inversion of stereochemistry.

[formula: see text] An efficient and unique route to the 5-7-6 core of guanacatepene A (1) is described. The installation of the desired stereochemistry at the C8 position was achieved via the desymmetrization of the cyclohexadienone by reductive ring closure of the seven-membered ring. That the closure of the seven-membered ring produced only the desired isomer is hypothesized to be a result of the more stable trans relationship between the C8 and C11 methyl groups.

Anti-Bacterial Agents↗

PubMed2002

Novel reactivity of SeO2 with 1,3-dienes: selenophene formation.

A novel and efficient method for the synthesis of selenophenes is disclosed. Selenophenes were synthesized in high yields in a single operation from 1,3-dienes containing a carbonyl group at the C-1 position and selenium dioxide. The bidirectional synthesis of selenophenes can also be demonstrated using this method. The selenophene is believed to form via a [4 + 2] cycloaddition between diene and selenium dioxide.

Alkenes↗