Lithium 2,2,6,6-tetramethylpiperidide (LTMP)-induced intramolecular cyclopropanation of unsaturated terminal epoxides provides an efficient and completely stereoselective entry to bicyclo[3.1.0]hexan-2-ols and bicyclo[4.1.0]heptan-2-ols. Further elaboration of C-5 and C-6 stannyl-substituted bicyclo[3.1.0]hexan-2-ols via Sn-Li exchange/electrophile trapping or Stille coupling generates a range of substituted bicyclic cyclopropanes. An alternative straightforward cyclopropanation protocol using a catalytic amount of 2,2,6,6-tetramethylpiperidine (TMP) allows for a convenient (1 g-7.5 kg) synthesis of bicyclo[3.1.0]hexan-2-ol and other bicyclic adducts. The synthetic utility of this chemistry has been demonstrated in a concise asymmetric synthesis of (+)-beta-cuparenone. The related unsaturated chlorohydrins also undergo intramolecular cyclopropanation via in situ epoxide formation.
Syntheses of chiral 6,15-dihydronaphtho[2,3-c]pentaphene derivatives of opposite configurations are reported. Starting from anthracene, the strategy involves two key steps: a Diels-Alder reaction on a prochiral dianthraquinone, and an enantiomeric resolution using (-)-menthol. The final molecules exhibit very strong optical activity, as shown by their circular dichroism spectra, and are examples of chiral facial amphiphiles. Their adsorption at the surface of single-walled carbon nanotubes (SWNTs) has also been studied, and has been found to occur preferentially on 0.8-1.0 nm diameter nanotubes among the population of a high-pressure CO conversion (HiPco) SWNT sample (0.8-1.2 nm). The synthesised facial amphiphiles act as nano-tweezers for the diameter-selective solubilisation of SWNTs in water. The expected optical activities of the SWNT samples solubilised by each of the chiral amphiphiles have been studied by circular dichroism spectroscopy, but the results are not yet conclusive.
Cyclopentane derivatives Q 0030Intramolecular Cyclopropanation of Unsaturated Terminal Epoxides and Chlorohydrins. -The LiTMP-induced reaction of unsaturated epoxides gives bicyclohexanols and bicycloheptanols with complete stereoselectivity. Several electrophilic trapping reactions as well as Stille cross-coupling reactions are performed with the stannyl-substituted products. The process can be also performed using BuLi and a substoichiometric amount of 2,2,6,6-tetramethylpiperidine. The latter method is demonstrated by the synthesis of β-cuparenone (XX) via bicyclohexanol (XIX), which is obtained from both epoxide (XVIII) and epichlorohydrin (XXI). -(HODGSON*, D. M.; CHUNG, Y. K.; NUZZO, I.; FREIXAS, G.; KULIKIEWICZ, K. K.; CLEATOR, E.; PARIS, J.-M.; J. Am. Chem. Soc. 129 (2007) 14, 4456-4462; Dep. Chem., Univ. Oxford, Oxford OX1 3QR, UK; Eng.) -Klein 35-069
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