Synthesis of cycloheptenes and higher homologues
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.
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.
Rh-catalyzed [5 + 2] cycloadditions of 1-(2-methyoxyethoxy)-1-vinylcyclopropane as a five-carbon component to alkynes provide cycloheptenones in many cases in minutes and in very good isolated yields. The procedure is readily conducted on a small or large scale.
P. A. Wender, A. J. Dyckman, C. O. Husfeld, M. J. C. Scanio, Org. Lett., 2000, 2, 1609-1611.
[ReBr(CO)3(thf)]2 catalyzes the reaction of a 1,3-dicarbonyl cyclic compound with an acetylene to give a medium-sized cyclic compound in excellent yield. By using isocyanide as an additive, the insertion of acetylenes into a carbon-carbon single bond occurs under mild conditions.
Y. Kuninobu, A. Kawata, K. Takai, J. Am. Chem. Soc., 2006, 128, 11368-11369.