Synthesis of cyclohexenes
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.
An efficient iron-catalyzed cross-coupling of primary alkyl Grignard reagents allows the use of alkenyl and aryl pivalates as electrophiles under mild conditions. The combination of an inexpensive and stable carboxylate electrophile and an iron catalyst would generate ample advantages.
B.-J. Li, L. Xu, Z.-H. Wu, B.-T. Guan, C.-L. Sun, B.-Q. Wang, Z.-J. Shi, J. Am. Chem. Soc., 2009, 131, 14656-14657.
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.
Reactions of internal alkynyl ketones under combined catalysts, AuCl3 / AgSbF6 or AuCl3 / AgOTf, afforded various, structurally diverse cyclic enones in good yields.
T. Jin, Y. Yamamoto, Org. Lett., 2007, 9, 5259-5262.
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.
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.
A rhodium-catalyzed cycloisomerization converts various acyclic enynes to their cyclic diene isomers with endoselectivity. Two different catalyst systems have been developed, which are effective in promoting the C-C bond-forming cyclization of enynes to furnish carbo- and heterocycles in good to excellent yield. The mechanism is discussed.
H. Kim, C. Lee, J. Am. Chem. Soc., 2005, 127, 10180-10181.
The Diels-Alder cycloaddition of a variety of cyclic and open-chained dienes to 2-methacrolein and 2-bromoacrolein resulted in good yields and excellent enantioselectivities by using a chiral indium complex.
Y.-Chua Teo, T.-P. Loh, Org. Lett., 2005, 7, 2539-2541.
Enantioselective Diels-Alder reactions catalyzed by a 2-[bis(3,5-bis-trifluoromethylphenyl) triethylsiloxymethyl]pyrrolidine salt in water provide Diels-Alder adducts with high exo selectivities and excellent enantioselectivities.
Y. Hayashi, S. Samanta, H. Gotoh, H. Ishikawa, Angew. Chem. Int. Ed., 2008, 47, 6634-6637.
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.
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. Gonzlez-Rodríguez, S. G. Rubín, L. Castedo, Carlos Saá, J. Am. Chem. Soc., 2006, 128, 9576-9577.
An enantioselective 1,4-diboration of cyclic dienes with a new taddol-derived phosphonite ligand and subsequent oxidation delivers 1,4-diols with excellent enantioselectivity, whereas homologation can be used to deliver chiral 1,6-diols.
K. Hong, J. P. Morken, J. Org. Chem., 2011, 76, 9102-9108.