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A heterocycle-to-heterocycle strategy is presented for the preparation of highly fluorescent and solvatochromic dibenzonaphthyridinones (DBNs) via methodology that leads to the formation of a tertiary, spiro-fused carbon center. A linear correlation between the results of photophysical experiments and time dependent density functional theory calculations was observed for the λ(max) of excitation for DBNs with varying electronic character.

We describe the (3 + 2) cycloaddition reaction of endocyclic N -silyl enamines and N , N' -cyclic azomethine imines. This process utilized the versatile endocyclic N -silyl enamine intermediates from the dearomative hydrosilylation of N -heteroarenes. The resulting tetracyclic pyrazolidinone structure was synthesized by a straightforward and atom-economical process. We also discussed the plausible origins of the different reactivity and endo/exo selectivity in terms of the structures of each proposed transition state. The successful gram-scale synthesis demonstrated the synthetic utility.

Described herein is the development of a new synthetic route to cyclic amidines from quinolines. The borane-catalyzed 1,4-hydrosilylation of quinoline was utilized for the dearomatization of the quinolines. The dearomatized enamine intermediate was subsequently reacted with a broad range of organic azides to produce the corresponding cyclic amidines (3,4-dihydroquinolinimines) via a [3 + 2] cycloaddition pathway. Preliminary mechanistic studies suggested that the hydride shift was involved during the cycloaddition.

A convergent asymmetric total synthesis of phorbaketal A was achieved in 10 steps through a Au(I)-catalyzed intramolecular spiroketalization reaction of an alkyne diol intermediate prepared from (R)-carvone and geranial. The spiroketalization reaction was regio- and stereoselective and was accompanied by isomerization of an exo-olefin into the trisubstituted olefin to form a unique spiroketal structure of phorbaketals.

Two new sesterterpenoids, phorbasones A (1) and B (2), were isolated from the Korean marine sponge Phorbas sp. Their complete structures were elucidated by spectral data and chemical reactions. Phorbasone A exhibited a positive effect on the calcium deposition activity in C3H10T1/2 cells. The biogenic origin of the core structure is believed to be through a novel rearrangement from the ansellone carbon structure.

Three new sesterterpenoids, phorbaketals A (1), B (2), and C (3) which have a spiroketal of the hydrobenzopyran moiety, were isolated from the Korean marine sponge Phorbas sp. Their complete structures were elucidated by spectral and chemical methods. They exhibited moderate cytotoxicity against human colorectal, hepatoma, and lung cancer cell lines. Furthermore, the cultivation of the bacterial fraction from the sponge afforded compound 1.