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The 1-azaspiro[4.4]nonane portion 11 of cephalotaxine was prepared via an intramolecular S N 2' substitution reaction followed by ozonolysis; condensation of 11 with the aromatic portion 13 gave compound 15; a Friedel-Crafts cyclization of 15 in polyphosphoric acid smoothly afforded the cephalotaxine skeleton 16. A single-crystal X-ray analysis of the HCl salt of 16 confirmed the structure of 16

Studies on the solution conformation of the cyclic depsipeptide antibiotic enopeptin A have been carried out using 2D NMR and molecular modelling techniques. The proton resonances of the antibiotic in DMSO-d6 have been assigned by the use of TOCSY and ROESY experiments. The interproton distance information obtained from the ROESY experiments have been used as the basis for elucidating the probable structures in solution. The restrained molecular dynamics technique was applied to calculate the structures in solution, and six resultant structures with fewer distance constraint violations were obtained that satisfy the experimental restraints very well. The conformation of the cyclic moiety of the molecule is well defined whereas the aliphatic chain segment is disordered.

A variety of substituted 1-oxaspiro[4.5]dec-6-ene and 1-oxaspiro[5.5]undec-7-ene systems have been prepared by utilizing Amberlyst-15-catalyzed SN2′ oxaspirocyclizations under mild reaction conditions (−20°C) in quantitative yields. In this process, a tertiary allylic alcohol serves as the precursor of π-allylic carbocation and the primary, secondary or tertiary alcohol within the same molecule serves as the nucleophile.

A variety of substituted 1-oxaspiro[4.4]non-6-ene, 1-oxaspiro[4.5]dec-6-ene, 6-oxaspiro[4.5]dec-1-ene and 1-oxaspiro[5.5]undec-7-ene systems have been prepared by utilizing Amberlyst-15-catalyzed intramolecular S N 2′ oxaspirocyclizations of secondary allylic alcohols under mild reaction conditions in quantitative yields. This oxaspirocyclization was applied to the total synthesis of theaspirane and theaspirone from β-ionone in five steps.

Three novel reactions for the synthesis of iso-condensed heteroaromatic pyrroles: (1) tandem intramolecular 1,3-dipolar cycloaddition and cycloreversion reaction; (2) phosphineimine-alkylidenemalonate cyclization reaction; (3) retromalonate addition reaction, are described. They can be used in acidic, neutral or basic conditions respectively. Iso-condensed heteroaromatic pyrroles, such as pyrrolo[3,4-b]indole 12, pyrrolo[3,4-b]pyridine 17, pyrrolo[3,4-c]pyridine 18, thieno[2,3-c]pyrrole 37, pyrrolo[3,4-b]pyrrole 40, pyrrolo[3,4-b]pyrazine 49, benzofuro[2,3-c]pyrrole 50, 1,2-bis[5-thieno[2,3-c]pyrrolyl]ethane 51, 1,4-bis[5-thieno[2,3-c]pyrrolyl]benzene 52, dipyrrolo[3,4-b;3′,4′-d]dipyrroles 55 and 56, benzotripyrroles 62–64, and thieno[3,4-c]pyrroles 67 and 73 are synthesized efficiently according to these methods.