Synthesis of 1,3-dienes
An efficient new route by coupling Grignard reagents and dienol phosphates in the presence of Fe(acac)3 allows a stereoselective preparation of terminal conjugated dienes.
G. Cahiez, V. Habiak, O. Gager, Org. Lett., 2008, 10, 2389-2392.
A mild, stereospecific cross-coupling of unsymmetrical 1,4-bissilyl-1,3-butadienes has been developed. A selective cross-coupling under mildly basic conditions afforded 4-aryl-1,3-dienylsilanes in excellent yield for a wide range coupling partners. The subsequent cross-coupling of the 4-aryl-1,3-dienylsilanes could be effected cleanly by the action of TBAF with electron-rich or electron-poor halides.
S. E. Denmark, S. A. Tymonko, J. Am. Chem. Soc., 2005, 127, 8004-8005.
A 1,4-elimination reaction of (E)-4-alkoxy-2-butenyl benzoates in the presence of KOH and a Pd catalyst gives vinyl ethers as intermediates that can be transformed to (2Z,4E)-2,4-pentadien-1-ols stereoselectively via a [1,2]-Wittig rearrangement. This subsequent [1,2]-Wittg rearrangement proceeds with retention of the stereochemistry.
T. Nakano, T. Soeta, K. Endo, K. Inomata, Y. Ukaji, J. Org. Chem., 2013, 78, 12654-12661.
The rhodium-catalyzed reaction of aryl boronic acids with internal alkynes and acrylates in water gives the domino coupling products. The reaction demonstrates that water offers the possibility to discover novel transformations.
T. Kurahashi, H. Shinokubo, A. Osuka, Angew. Chem. Int. Ed., 2006, 45, 6336-6338.
Exposure of aldehydes or α-ketoesters to acetylene and hydrogen gas at ambient temperature and pressure in the presence of a cationic rhodium catalysts provides the products of a formal carbonyl Z-butadienylation. These multicomponent couplings represent the first use of acetylene gas in metal-catalyzed reductive C-C bond formation.
J. R. Kong, M. J. Krische, J. Am. Chem. Soc., 2006, 128, 16040-16041.
Catalytic hydrogenation of 1,3-enynes in the presence of ethyl glyoxalate at ambient pressure and temperature using a rhodium catalyst modified by (R)-(3,5-tBu-4-MeOPh)-MeO-BIPHEP results in highly regio- and enantioselective reductive coupling to furnish the corresponding α-hydroxy esters.
Y.-T. Hong, C.-W. Cho, E. Skucas, M. J. Krische, Org. Lett., 2007, 9, 3745-3748.
Highly enantioselective direct catalytic reductive couplings of 1,3-enynes to activated ketones such as ethyl pyruvate have been achieved by using chirally modified cationic rhodium catalysts in the presence of hydrogen to afford dienylated α-hydroxy esters with exceptional levels of regio- and enantiocontrol.
J.-R. Kong, M.-Y. Ngai, M. J. Krische, J. Am. Chem. Soc., 2006, 128, 718-719.
Hydroboration of a variety of 1-bromo-1-acetylenes with dicyclohexyl borane, reaction with t-BuLi, and transmetalation to zinc generates a (Z)-disubstituted vinylzinc reagent. In situ reaction of this reagent with aldehydes generates (Z)-disubstituted allylic alcohols in high yields.
S.-J. Jeon, E. L. Fischer, P. J. Carroll, P. J. Walsh, J. Am. Chem. Soc., 2006, 128, 9618-9619.