Synthesis of cyclopentenes
The reaction of organocerium reagents, generated in situ from aryl and heteroaryl lithium compounds, with cycloalkanones proceeds cleanly to provide alkoxides. Addition of MsCl or SOCl2 with DBU gave aryl-substituted cycloalkenes in good yields. A short total synthesis of (±)-laurokamurene B is described.
J. Tallineau, G. Bashiardes, J.-M. Coustard, F. Lecornué, Synlett, 2009, 2761-2764.
In situ generation of allylic boronates by iridium-catalyzed borylation of cyclic alkenes in the presence of additives, such as methylimidazole and DBU, followed a reaction with aldehydes allows the synthesis of stereodefined homoallylic alcohols. Cycloalkenes without additives as well as acyclic substrates gave vinylic boronates, which were coupled with organohalides in a Suzuki-Miyaura sequence.
V. J. Olsson, K. J. Szabó, J. Org. Chem., 2009, 74, 7715-7723.
A new phosphoramidite is an effective chiral ligand in a palladium-catalyzed asymmetric Mizoroki-Heck reaction using benzyl electrophiles. The reaction is compatible with polar functional groups and can be readily scaled up. Several cyclic olefins worked well as olefin components.
Z. Yang, J. Zhou, J. Am. Chem. Soc., 2012, 134, 11833-11835.
In an asymmetric intermolecular Heck reaction, various cyclic olefins coupled with aryl and vinyl bromides in high enantioselectivity. Only bisphosphine oxides on a spiro backbone formed highly stereoselective Pd catalysts. The use of alkylammonium salts and alcoholic solvents were essential to promote halide dissociation from the arylpalladium intermediate.
C. Wu, J. Zhou, J. Am. Chem. Soc., 2014, 136, 650-652.
Copper-catalyzed arylcarbocyclization of alkynes with diaryliodonium salts provides carbocycles with good step-economy through C-C bond formation on an inert C(sp3)-H bond. Theoretical studies revealed an interesting Cu-catalyzed concerted pathway of the C-C bond formation.
J. Peng, C. Chen, J. Chen, X. Su, C. Xi, H. Chen, Org. Lett., 2014, 16, 3776-3779.
An allylic alkylation/ring-closing metathesis domino process is catalyzed by the combination of a palladium and a ruthenium catalyst. This study demonstrates the compatibility of the two catalytic systems. Evidence for Grubbs' catalysts activity in allylic alkylation is also reported.
C. Kammerer, G. Prestat, T. Gaillard, D. Madec, G. Poli, Org. Lett., 2008, 10, 405-408.
A highly enantioselective Rh-catalyzed asymmetric allylic substitution allows the desymmetrization of meso cyclopent-2-ene-1,4-diethyl dicarbonates. Depending on the ligand, each of two regioisomeric products can be obtained in good yield and excellent enantioselectivity. Whereas bisphosphine P-Phos ligands form trans-1,2-arylcyclopentenols, Segphos ligands lead predominantly to trans-1,4-arylcyclopentenols.
F. Menard, D. Perez, D. S. Roman, T. M. Chapman, M. Lautens, J. Org. Chem., 2010, 75, 4056-4068.
A P-cyclohexyl substituted ferrocenophane catalyst affords high levels of asymmetric induction in the organocatalytic [3 + 2] annulation reaction between allenes and electron-poor olefins.
A. Voituriez, A. Panossian, N. Fleury-Brégeot, P. Retailleau, A. Marinetti, J. Am. Chem. Soc., 2008, 130, 14030-14031.
A nucleophile-catalyzed asymmetric [3+2] cycloaddition of allenes with enones is described. The method has also been applied to reactions of trisubstituted olefins, thereby generating quartenary and tertiary stereocenters.
J. E. Wilson, G. C. Fu, Angew. Chem. Int. Ed., 2006, 45, 1426-1429.
Palladium-catalyzed annulation reactions of conjugate acceptors and allenyl boronic ester provide substituted cyclopentenes in high yields and diastereoselectivities, including polycyclic lactone and lactam products. Reactions are hypothesized to initiate by conjugate addition of a nucleophilic propargylpalladium complex.
B. L. Kohn, E. R. Jarvo, Org. Lett., 2011, 13, 4858-4861.
An efficient method allows a stereospecific synthesis of trans-substituted cyclopentene derivatives via the ring-opening rearrangement of readily available MCP alkenyl derivatives in good yields. This transformation might proceed through a fast concerted pericyclic process rather than a simple radical pathway or an ionic pathway.
X.-Y. Tang, M. Shi, J. Org. Chem., 2010, 75, 902-905.
An efficient cycloallylation of mono-enone mono-allylic carbonates is achieved upon exposure to tributylphosphine and 1 mol % Pd(Ph3P)4. This transformation combines the nucleophilic features of the Morita-Baylis-Hillman reaction with the electrophilic features of the Trost-Tsuji reaction.
B. G. Jellerich, J.-R. Kong, M. J. Krische, J. Am. Chem. Soc., 2003, 125, 7758-7759.
An organomediated, intramolecular Morita-Baylis-Hillman reaction of molecules bearing allylic leaving groups as the electrophilic partner provided a facile, high yielding, straightforward synthesis of densely functionalized cyclic molecules.
M. E. Krafft, T. F. N. Haxell, J. Am. Chem. Soc., 2005, 127, 10168-10169.
Conversion of unsaturated ketones and aldehydes derived from the cycloisomerization of primary and secondary propargyl diynols in the presence of [CpRu(CH3CN)3]PF6 to 1-azatrienes and a subsequent electrocyclization-dehydration provides pyridines with excellent regiocontrol.
B. M. Trost, A. C. Gutierrez, Org. Lett., 2007, 9, 1473-1476.
An enantioselective synthesis of α,α-disubstituted cyclopentenes proceeds via a chiral enol generated in situ from an α,β-unsaturated aldehyde and a chiral N-heterocyclic carbene catalyst. This reactive enol undergoes addition to one of two enantiotopic ketones to afford an optically active β-lactone. Depending on the substitution, a decarboxylation produces the cyclopentene products in high ee.
M. Wadamoto, E. M. Philipps, T. E. Reynolds, K. A. Scheidt, J. Am. Chem. Soc., 2007, 129, 10098-10099.
An oxidation-methylenation one-pot procedure in the presence different catalysts produced terminal alkenes in high yields. A methylenation-ring-closing process for the synthesis of cyclic alkenes from carbonyl derivatives was even expanded with an initial oxidation to allow the use of alcohols as substrates.
H. Lebel, V. Paquet, J. Am. Chem. Soc., 2004, 126, 11152-11153.
N-Heterocyclic carbene/Lewis acid cooperative catalysis provides access to cis-1,3,4-trisubstituted cyclopentenes from enals and chalcone derivatives with high levels of diastereoselectivity and enantioselectivity. The presence of Ti(OiPr)4 as Lewis acid enables an efficient substrate preorganization, which translates into high levels of diastereoselectivity.
B. Cardinal-David, D. E. A. Raup, K. A. Scheidt, J. Am. Chem. Soc., 2010, 132, 5345-5347.
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.
The GaCl3-catalyzed skeletal reorganization of enynes is simple and provides a diverse range of dienes in good to high yields. The reaction of enynes proceeds in a stereospecific manner with respect to the geometry of the olefin moiety.
N. Chatani, H. Inoue, T. Kotsuma, S. Murai, J. Am. Chem. Soc., 2002, 124, 10294-10295.
Cycloalkenes can be efficiently prepared by a new Ru-catalyzed decarbonylative cyclization of terminal alkynals. Under appropriate conditions, cycloisomerizations to conjugated aldehydes may be observed. Both processes involve catalytic Ru vinylidenes.
J. A. Varela, C. González-Rodríguez, S. G. Rubín, L. Castedo, Carlos Saá, J. Am. Chem. Soc., 2006, 128, 9576-9577.
TFA-promoted exo carbocyclizations of nonterminal alkynals gave good to excellent yields of exo cycloalkenones. On the other hand, terminal 5-alkynals gave endo carbocyclizations to cyclohexenones. These carbocyclizations can be considered as tandem alkyne hydration/aldol condensation processes.
C. González-Rodríguez, L. Escalante, J. A. Varela, L. Castedo, C. Sáa, Org. Lett., 2009, 11, 1531-1533.
A sequence of Pd-catalyzed haloallylation of alkynes, Pd-catalyzed cross-coupling, and Ru-catalyzed ring-closing metathesis enables a short approach to various 1,2-disubstituted cyclopentadienes. The scope of the method is broad.
N. Topolovčan, I. Panov, Martin Kotora, Org. Lett., 2016, 18, 3634-3637.
Trapping of β,γ-alkynyl aldehydes, generated in situ by treatment of alkynyloxiranes with a catalytic amount of Sc(OTf)3 or BF3·OEt2, 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.
Iodocyclopentenes are formed at room temperature upon iodonium-promoted 5-endo-dig carbocyclization of δ-alkynyl-β-ketoesters with I2. Cyclizations involving terminal and substituted (alkyl, aryl, Br, I) alkynes were accessed.
J. Barluenga, D. Palomas, E. Rubio, J. M. Gonzáles, Org. Lett., 2007, 9, 2823-2826.
A sequence of two gold(I)-catalyzed isomerization steps allows the synthesis of functionalized acetoxy bicyclo[3.1.0]hexenes from 5-en-2-yn-1-yl acetates. Acetoxy bicyclo[3.1.0]hexene products can be further transformed to 2-cycloalkenones by simple methanolysis.
A. Buzas, F. Gagosz, J. Am. Chem. Soc., 2006, 128, 12614-12615.