Synthesis of cyclopentanols
Ruthenium carbene complexes catalyze ring closing metathesis (RCM) and a subsequent hydrogenation after activation with sodium hydride. Hydrogenation of cyclopentenols proceeds smoothly at ambient temperature and under 1 atm of hydrogen in toluene.
B. Schmidt, M. Pohler, Org. Biomol. Chem., 2003, 1, 2512-2517.
Cyclizations of allenyl aldehydes and intermolecular couplings of allenes and aldehydes provide homoallylic alcohols. The couplings and cyclizations involve the use of diorganozinc reagents as reducing agents and Ni(COD)2 as the catalyst.
M. Song, J. Montgomery, Tetrahedron, 2005, 61, 11440-11448.
The CoI2(dppe)-catalyzed diastereoselective reductive [3 + 2] cycloaddition of allenes and enones gives cyclopentanols in very good yields in the presence of zinc, zinc iodide, and water.
H.-T. Chang, T. T. Jayanth, C.-H. Cheng, J. Am. Chem. Soc., 2007, 129, 4166-4167.
An intermolecular pinacol coupling of aromatic or aliphatic carbonyl compounds catalyzed by a complex of samarium diiodide (SmI2) with tetraglyme in the presence of Me2SiCl2 and Mg is described. High diastereoselectivity has been achieved in reactions with aliphatic and aromatic aldehydes. De values of up to 99% have been achieved in intramolecular pinacol coupling reactions.
H. C. Aspinall, N. Greeves, C. Valla, Org. Lett., 2005, 7, 1919-1922.
An efficient lithium amide-induced intramolecular cyclopropanation of bishomoallylic and trishomoallylic epoxides is described. The methodology is used in an asymmetric synthesis of sabina ketone.
D. M. Hodgson, Y. K. Chung, J.-M. Paris, J. Am. Chem. Soc., 2004, 126, 8654-8655.
Trapping of β,γ-alkynyl aldehydes, generated in situ by treatment of alkynyloxiranes with a catalytic amount of Sc(OTf)3 or BF3ˇOEt2, by a variety of allyl nucleophiles affords homopropargylic homoallylic alcohols in good yield and selectivity. Subsequent enyne metathesis gives functionalized vinylcyclopentenols.
L. Wang, M. L. Maddess, M. Lautens, J. Org. Chem., 2007, 72, 1822-1825.
Stirring α,β-unsaturated α-diketones in the presence of activated silica gel results in cyclization to α-hydroxycyclopentenones in good yield. The reaction is sensitive to the mode of stirring and proceeds more rapidly in the presence of triethylamine consistent with a Nazarov reaction proceeding through the enol tautomer.
E. A. Uhrich, W. A. Batson, M. A. Tius, Synthesis, 2006, 2139-2142.
A [6 + 2] annulation that involves the combination of β-alkenoyl acylsilanes and a vinyllithium derivative enables in one operation and a stereoselective manner the construction of eight-membered ring systems containing useful functionalities for further synthetic elaboration from readily available six- and two-carbon components.
K. Takeda, H. Haraguchi, Y. Okamoto, Org. Lett., 2003, 5, 3705-3707.