The synthesis and reactions of 2,11-diselena[3,3]metacyclophanes. An investigation of the selenoxide elimination route to metacyclophane-1,8-dienes

Abstract

. Can. J. Chem. 58, 1398Chem. 58, (1980. 2,ll-Diselena[3,3]metacyclophane and its 9,18-dimethyl derivative are prepared in ca. 7% yield from Na,Se and xylylene bromide. Wittig rearrangement and benzyne induced Stevens rearrangement gave the ring contracted [2,2]metacyclophane derivative. Attempted selenoxide elimination to produce metacyclophane-diene failed. The lHmr spectra of the selenametacyclophane indicate that the syn-conformer is the more stable. A general synthesis of aryl-alkenes in an 80% yield starting from benzyl phenyl selenide, alkylation with an alkyl halide, and then selenoxide elimination is given. REGINALD H. MITCHELL. Can. J. Chem. 58,1398Chem. 58, (1980. On a prepare le disC1Cna-2,11 [3,3] Introduction and Boekelheide (9) have shown that sulfoxides Dithiacyclophanesl have attracted much atten-1Kb and 1Ka give d i h~d r o~~r e n e 3b (34%) and tion in recent years both because of their interesting PYrene 4 (37%) respectively on pyrolysis under fluxional properties (1) and because of their ready vacuum. The internal hydrogen substituents of the conversion into both the cyclophanes themselves initially formed 3a were evidently lost at the tem-(2) and into many novel derived polycyclic aroma-perature of the pyrolysis-Indeed it has been shown tic compounds (3). However, until our initial report (6) that such hydrogens undergo migration out of (4), the andagous diselenaphanes were unknown.the Centre of the ring at temperatures above 6O0C, ~h~~~ was some considerable incentive to inves-and hence the possibility that the selenoxide 1La or tigate the properties of such compounds because of 1Na might undergo elimination at room tempera-

Selenenate Anions (PhSeO−) as Organocatalyst: Synthesis of trans‐Stilbenes and a PPV Derivative

“…It is noteworthy that methoxy-containing stilbenes are potential anticancer agents. As shown in Scheme 2, n-dodecanyl phenyl selenoxide [17] and dimethyl selenoxide [18] worked well under the standard reaction conditions, with the exception of preheating the precatalysts at 50°C for 20 min. Heterocyclic stilbene derivatives are reported to exhibit interesting photophysical properties.…”

“…It is known that the anion PhSeO 2 À reacts with Me 3 SiÀ Cl to form O (SiMe 3 ) 2 and (PhSeO) 2 O, [21] while PhSe À undergoes silylation to give PhSeSiMe 3 . [1e,10a] Therefore, to probe the reactivity of this intermediate, we conducted in situ studies by oxidation of benzylated benzyl phenyl selenide (PhSeCH(Ph)CH 2 Ph) [17] using meta-chloroperoxybenzoic acid (m-CPBA) (Scheme 3b). It is surprising that a mixture of isomers was obtained, given that only trans-stilbene is observed in all the other cases in this study (from intermediate C, Scheme 1).…”

“…Based on the proposed mechanism shown in Scheme , different selenoxides were synthesized and tested to evaluate their viability as precatalysts in the dehydrohalogen coupling of stilbenes. As shown in Scheme , n ‐dodecanyl phenyl selenoxide and dimethyl selenoxide worked well under the standard reaction conditions, with the exception of preheating the precatalysts at 50 °C for 20 min. This approach led to conversion of benzyl chloride to trans ‐stilbene with respectable yields (80% and 72%, respectively).…”

“…Attempts to identify the benzylated selenoxide intermediate PhSe(=O)CH(Ph)CH 2 Ph from the catalytic reactions (Figure , C ) failed, presumably due to its rapid decomposition to form trans ‐stilbene and benzeneselenenic acid . Therefore, to probe the reactivity of this intermediate, we conducted in situ studies by oxidation of benzylated benzyl phenyl selenide (PhSeCH(Ph)CH 2 Ph) using meta ‐chloroperoxybenzoic acid ( m ‐CPBA) (Scheme b). Accordingly, after oxidation, trans ‐stilbene was isolated in 78% yield, but PhSe(=O)CH(Ph)CH 2 Ph) ( C ) was not observed in this process.…”

Selenolate Anion as an Organocatalyst: Reactions and Mechanistic Studies

“…Reactions conditions: (0.2 mmol aryl chloride, 1.0 equiv), RT. b) KN(SiMe 3 ) 2 (3.0 equiv for entries 1-7 and 13, 1.5 equiv for entries [8][9][10][11][12]. c) AY (assay yields) determined by 1 H NMR spectroscopy using CH 2 Br 2 as an internal standard.…”