Categories: C=C Bond Formation >
Synthesis of allenes by nucleophilic 1,3-substitution
A chemoselective isomerization of secondary-type propargylic alcohols under Appel-type reaction conditions in the presence of Ph3P, CBr4 and additives gives allenic bromides, propargylic bromides and brominated dienes.
N. Sakai, T. Maruyama, T. Konakahara, Synlett, 2009, 2105-2106.
With a suitable combination of N-heterocyclic carbene precatalyst, base, and fluorine reagent, a fluorination of alkynals proceeded smoothly to yield a wide range of α-fluoroallenoates with excellent chemoselectivity. α-Fluorinated allenoates are versatile synthetic intermediates toward other useful fluorine-containing building blocks.
X. Wang, Z. Wu, J. Wang, Org. Lett., 2016, 18, 576-579.
A copper-catalyzed synthesis of benzyl-, allyl-, and allenyl-boronates from benzylic, allylic, and propargylic alcohols, respectively, exhibits a broad reaction scope and high efficiency under mild conditions. Preliminarily mechanistic studies suggest that nucleophilic substitution is involved in this reaction.
L. Mao, K. J. Szabó, T. B. Marder, Org. Lett., 2017, 19, 1204-1207.
Bimetallic Pd/Cu and Pd/Ag catalytic systems enable a stererospecifically borylation of propargylic alcohol derivatives via formal SN2′ pathways to give allenyl boronates. Opening of propargyl epoxides leads to 1,2-diborylated butadienes probably via en allenylboronate intermediate.
T. S. N. Zhao, Y. Yang, T. Lessing, K. J. Szabo, J. Am. Chem. Soc., 2014, 136, 7359-7542.
The silicon nucleophile generated by copper(I)-catalyzed Si-B bond activation allows several γ-selective propargylic substitutions. Chloride as a leaving groups is superior in linear substrates, and the phosphate group produces superb γ-selectivity in α-branched propargylic systems, and enantioenriched substrates react with excellent central-to-axial chirality transfer.
D. J. Vyas, C. K. Hazra, M. Oestreich, Org. Lett., 2011, 13, 4462-4465.
A Rh-catalyzed coupling reaction between propargylic carbonates and a silylboronate affords allenylsilanes in high yields. The reaction tolerates various functional groups and proceeds with excellent chirality transfer.
H. Ohmiya, H. Ito, M. Sawamura, Org. Lett., 2009, 11, 5618-5620.
A Cu(O-t-Bu)-Xantphos catalyst system was effective for the preparation of various allenylboronates with different substitution patterns, those with functional groups, and an axially chiral one. A Lewis acid promoted stereoselective addition of allenylboronates to aldehydes leads to homopropargylic alcohols.
H. Ito, Y. Sasaki, M. Sawamura, J. Am. Chem. Soc., 2008, 130, 15774-15775.
A facile and efficient copper-catalyzed direct C-P cross-coupling of unprotected propargylic alcohols with P(O)H compounds provides valuable allenylphosphoryl frameworks with operational simplicity and high step- and atom-economy under ligand-, base-, and additive-free conditions.
G. Hu, C. Shan, W. Chen, P. Xu, Y. Gao, Y. Zhao, Org. Lett., 2016, 18, 6066-6069.
A new, efficient method based on a palladium(0)-catalyzed reaction of propargylic derivatives with various phosphorus nucleophiles produces allenylphosphonates and their analogues with defined stereochemistry in the allenic and the phosphonate moiety.
M. Kalek, T. Johansson, M. Jezowska, J. Stawinski, Org. Lett., 2010, 12, 4702-4704.
A TBHP/TBAI-mediated reaction of propargyl alcohols with sulfonyl hydrazides in the presence of HOAc provides allenyl sulfones in good yields in a short reaction time via HOAc-promoted sulfonohydrazide intermediate formation, sequential C-O, C-N, and N-S bond cleavage, and C-S bond formation. This reaction shows highly functional group compatibility and excellent regioselectivity.
Z. Yang, W.-J. Hao, S.-L. Wang, J.-P. Zhang, B. Jiang, G. Li, S.-J. Tu, J. Org. Chem., 2015, 80, 9224-9230.