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.
The stereospecific lithiation of diastereomeric phenylpropylene oxides has been studied as well as the trapping reaction with electrophiles. The reduction of the cis-alpha-benzoylpropylene oxide to give prevalently the anti-epoxy alcohol has been investigated as well.
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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