Showing papers by "Nobuaki Taniguchi published in 1994"

Asymmetric total synthesis of tacamonine (pseudovincamone I) via radical cyclization

Abstract: The radical cyclizations of (±)-(E)-3-((2-(bromomethyl)butoxy)carbonyl)- prop-2-enoates (11) and (12) and (±)-ethyl (E)-3-{N-[2-(bromomethyl)- butyl]-N-[2-(3-indolyl)ethyl]carbamoyl}prop-2-enoate (25) were carried out with (TMS) 3 SiH or Bu 3 SnH in the presence of AIBN. (-)-(2S)-2- ((tert-Butyldimethylsilyloxy)methyl)butan-1-ol (6), which was prepared by two different methods, was converted into (+)-25. The radical cycli- zation of(+)-25 produced piperidinone (18) as a diastereomeric mixture, which was transformed into tacamonine (1)

A Total Synthesis of (±)-Tacamonine (Pseudovincamone I) through Radical Cyclization

Abstract: The radical cyclization of the bromo ester (11), prepared from 2-hydroxymethylbutan-1-ol (7), giving the diastereoisomeric mixture of lactones (12) was examined under various conditions. Treatment of the bromo ester (17), derived from 7, with tris(trimethylsilyl)silane in the presence of 2,2-azoisobutyronitrile provided the epimeric mixture of lactams (18), convertible to (±)-tacamonine (pseudovincamone I) (1) in three steps

Deconjugation of α,β‐Unsaturated Esters and an Intramolecular Michael Reaction of Bis‐α,β‐unsaturated Esters with Trialkylsilyl Trifluoromethanesulfonate in the Presence of Tertiary Amine: Synthesis of (.+‐.)‐Ricciocarpin A.

Abstract: Treatment of the α,β-unsaturated esters 1, 6 and 8 with trialkylsilyl trifluoromethanesulfonate in the presence of a tertiary amine gave, via silyl dienol ethers, the corresponding deconjugated esters 3, 7 and 9 as the major products, respectively. Reaction of bis-α,β-unsaturated esters 12a and 12b with a trialkylsilyl trifluoromethansulfonate in the presence of a tertiary amine caused an intramolecular Michael reaction to produce the cyclopentanes 14a and 20a and the cyclohexanes 14b and 20b. Bicyclic compounds 21a and 21b formed by tandem Michael–Dieckmann or intramolecular Diels–Alder reaction were concurrently obtained. The cyclohexane derivative 14b was converted into the racemate of a sesquiterpene, (±)-ricciocarpin A 22.

Synthesis of Polycyclic Cyclobutane Derivatives by Tandem Intramolecular Michael-Aldol Reaction Under Two Complementary Conditions; TBDMSOTf-Et3N and TMSI-(TMS)2NH.

Abstract: The treatment of α,β-unsaturated esters having a ketone function at an appropriate position with either TBDMSOTf in the presence of Et 3 N or TMSI in the presence of (TMS) 2 NH provided, via a tandem intramolecular Michael-aldol reaction sequence, several different types of cyclobutane derivatives. The two reaction conditions were complementary. Tricyclo[4.2.1.03-8]nonanes 34 and 35, tricyclo[5.1.1.0 3,8 ]nonane 40, tricyclo[5.4.0.0 3,7 ]undecane 51, tetracyclo[5.4.0.0 3,7 .0 9,11 ]undecane 45, and the bicyclo[3.2.0]heptanes 36, 57, and 38, which have structures either partially or completely similar to those of endiandric acids A (1a), B (1b), and C (2), trihydroxydecipiadiene (3), lintenone (4), italicene (3), and filifolone (6), were stereoselectively synthesized by the tandem reaction