Carbocyclic cis-[1.1.1]-tris-σ-homobenzenes - Syntheses by triple epoxide → cyclopropane conversions, structural data, [σ2s+σ2s+σ2s] cycloreversions
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Authors
By triple epoxide → cyclopropane transformation starting from cis-benzene trioxide the 3α,6α,9α-tris(TIPS-ethynyl) (1b), -tris(alkoxycarbonyl) (1d, e), -tricyano (1f), and -tris(ammoniomethyl) (1j) derivatives of the still elusive parent cis-[1.1.1]-tris-σ-homobenzene (1a) have been synthesized. Out of a number of carbon nucleophiles tested, a weakly basic mixed cyanocuprate of Li-TIPS-propyne proved the reagent of choice: Eliminations were largely avoided, the scyllo [*]-2,4,6-tris(TIPS-propargyl)cyclohexane-1,3,5-triol (13a), obtained in a stereoselective one-pot threefold epoxide opening (up to 69%), allowed the pertinent functional group manipulations. The selectivity of the base-induced triple cyclopropane ring closure in the flexible cyclohexane precursors strongly depends on the activating groups and is promoted by fixation of the "all-axial" conformation as an adamantoid orthophosphate. The ΔG ≠ values determined for the generally neat 3σ → 3π isomerizations [28.5 (1e), 29.0 (1f), 22.6 (1j) kcal mol -1] are in line with concerted reaction courses ([σ2s+σ2s+σ2s]). For the trinitrile 1f an X-ray structure analysis confirmed a nearly planar cyclohexane ring and a relatively large cyclohexane/cyclopropane interplanary angle (113°).
Original language | English |
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Journal | Liebigs Annalen - recueil |
Volume | 1997 |
Issue number | 5 |
Pages (from-to) | 967-989 |
Number of pages | 23 |
ISSN | 0947-3440 |
DOIs | |
Publication status | Published - 01.05.1997 |
Externally published | Yes |
- Chemistry
- cis-[1.1.1]-Tris-σ-homobenzenes, Substituent effects, [σ2s+σ2s+σ2s] Cycloreversions