A Novel C₃‐Symmetric Triol as Chiral Receptor for Ammonium Ions

Abstract

The enantiopure C3‐symmetric syn‐benzotriborneol was efficiently obtained in an eight‐step route. Of particular interest from a synthetic point of view are the potassium tert‐butoxide promoted bromination of camphor hydrazone (4) and the observation that the protecting groups influence the syn/anti diasteroselectivity of the cyclotrimerization reaction of 12–14. Complexation studies in deuteriochloroform revealed the capability of the cyclotrimer syn‐1 to act as host for ammonium ions, and in particular, the efficient chiral recognition of the two enantiomers of (1‐phenylethyl)ammonium chloride. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Gas Hosting in Enantiopure Self‐Assembled Oximes

“…The trioxime scaffold 3 was readily prepared in two steps from the previously reported (+)-syn-benzotriborneol (1), [12] with the first step being an oxidization following the standard Swern protocol. [13] Scaffold 2 was then condensed with hydroxylamine according to a well-known procedure, [14] which led to the formation of the expected syn-benzotri(camphor oxime) (3, Scheme 1).…”

Highly diastereoselective synthesis of a novel functionalized benzocyclotrimer

“…The mixture of diastereomers was dehydrobrominated with potassium tert-butoxide in THF, 26 to afford the alkenyldibromide 8 in good yield (93%) (Scheme 1). The key reagent 9 for the cyclotrimerization was obtained either by proton abstraction of halide 6 with lithium diisopropylamide (LDA) 11,13,[27][28][29][30][31][32][33] or by removal of one of the bromine atoms of the dibromide 8 with nbutyl lithium 30,31,34,35 followed by a trans-metalation reaction with trimethyltin chloride in 96% yield in both cases. The high chemoselectivity of removal of the bromine atom in 8 was surprisingly: indeed, the bromine atoms attached to the aromatic ring remained completely unaffected.…”

“…1 This behaviour has been previously observed when a ligating group is present in the monomer. 37,38,11,32 It is likely that the oxa-bridge in the dihydronaphthalene is responsible for the high reverse selectivity, by means of coordination with copper. The separation of the two isomers was easily accomplished by chromatography on neutral alumina and the major syn-1 isomer was available for further functionalization and supramolecular studies.…”

“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15] Amongst these, benzocyclotrimers bearing aromatic rings are characterized by large stiff cavities. The cavities are particularly deep and suitable for supramolecular applications in case of the more symmetrical syn-diastereomer, which is generally obtained in lower yields.…”

Bifunctional Rhenium Complexes for the Catalytic Transfer‐Hydrogenation Reactions of Ketones and Imines

“…Recently, benzocyclotrimers have also found applications in supramolecular chemistry, by furnishing appropriate scaffolds for the preparation of pH‐sensitive molecular baskets13 and receptors for C 60 14. Enantiopure (+)‐benzotriborneol syn ‐ 4 discriminates chiral ammonium ions15 and has high affinity to water 16. The diverse reactivity of the carbonyl group in enantiopure cyclotrimers is extremely appealing for applications in supramolecular chemistry, as demonstrated in the case of (+)‐benzotricamphor syn ‐ 5 , which was conveniently employed for the synthesis of (+)‐benzotricamphor tris‐oxime syn ‐ 6 , which self‐assembles into a dimeric unit with a cavity suitable for hosting N 2 , O 2 and CH 4 ,17 and (+)‐cage syn ‐ 7 , which can selectively bind gases like acetylene with respect to ethylene and ethane 18…”