5-exo-Dig versus 6-endo-dig oxycyclizations of alkynols having an internal triple bond catalyzed by PdCl2, followed by methoxycarbonylation of the resulting vinylpalladium intermediates, are described. With an aim toward the total synthesis of polymaxenolides, a hybrid marine natural product containing a dihydropyran substructure, a model alkynol having the africane-type sesquiterpenoid skeleton was treated with PdCl2 and 1,4-benzoquinone in MeOH under an atmosphere of CO (balloon) to afford the desired 6-endo-dig oxycyclization–methoxycarbonylation product.

Isopropyl carbamates derived from benzylamines provide isoindolinones by treatment with phosphorus pentoxide at room temperature. Utility of this Bischler–Napieralski-type cyclization and a new mechanism involving a carbamoyl cation for rationalization of this smooth conversion are discussed.

Ansa compounds are gifts from microbes with intriguing molecular structures and highly potent bioactivities. One of the ansa compounds, kendomycin, has an oxa-metacyclophane skeleton with a quinone methide core and a fully substituted tetrahydropyran ring. Beyond a common synthetic strategy for construction of the ansa skeleton (i.e., elongation of an alkyl chain from an aromatic core followed by macrocyclization), we challenged a new method for construction of the ansa skeleton via simultaneous macrocyclization and benzannulation (using an intramolecular Dötz benzannulation). Understanding the reactivity of various Fischer-type ω-alkynyloxy chromium carbene complexes with kendomycin analogue syntheses led to achievement of the total synthesis of kendomycin. Investigations of structure–activity relationships revealed the need for an ansa skeleton for antimicrobial activity. Therefore, we envisage that this intramolecular Dötz benzannulation will enable divergent syntheses of ansa compounds which have important bioactive potential.

A racemic total synthesis of the sesquiterpenoid unit of the hybrid marine natural product polymaxenolide has been achieved based on a three-component assembly followed by ring-closing metathesis as the key steps. However, the spectral data of our product synthesized from Δ9(15)-africanene by epoxidation were not identical with those of the natural product named epoxyafricanane. The structure confirmation of the synthetic nominal epoxyafricanane is described.

One-step formation of the ansa-skeleton realized the synthesis of kendomycin, an ansa-type quinone methide. The Fischer carbene complex derived from the ansa-chain portion was subjected to the intramolecular Dötz benzannulation to afford the desired oxametacyclophane with exclusive regioselectivity. Subsequent Claisen rearrangement, ortho oxidation of the resulting phenol derivative, and mild transformation from p-quinone to p-quinone methide on a silica gel plate furnished kendomycin.

The lactonamycin model aglycon 4 was synthesized from the trihalogenated benzene derivative 10. Ethynyltetraol 6 was prepared from 10 via carbon elongations, oxidative demethylation, a cycloaddition reaction with the diene derived from homophthalic anhydride, and dihydroxylation. Final E- and F-ring constructions from 6 were realized via a palladium-catalyzed cyclization−methoxycarbonylation, a stereoselective methanol addition, and lactonization, leading to the production of 4.