Categories: CC Bond Formation >
Synthesis of terminal alkynes
A highly convenient way to perform the synthesis of alkynes from aldehydes utilizes a new in situ preparation of dimethyldiazomethylphosphonate. As a consequence a commercially available reagent can now be used, circumventing a disadvantage of earlier protocols.
G. J. Roth, B. Liepold, S. G. Müller, H. J. Bestmann, Synthesis, 2004, 59-62.
A direct conversion of activated primary alcohols into terminal alkynes through a sequential one-pot, two-step process involving oxidation with manganese dioxide and then treatment with the Bestmann-Ohira reagent proceeds efficiently under mild reaction conditions with a range of benzylic, heterocyclic and propargylic alcohols.
E. Quesada, R. J. K. Taylor, Tetrahedron Lett., 2005, 46, 6473-6476.
Esters and Weinreb amides undergo reduction to the corresponding aldehydes using DIBAL-H followed by same pot conversion to terminal alkynes utilizing the Bestmann-Ohira reagent in good to excellent yields.
H. D Dickson, S. C. Smith, K. W. Hinkle, Tetrahedron Lett., 2004, 45, 5597-5599.
Terminal and internal acetylenes were obtained in good to excellent isolated yields from carbonyl compounds by converting the carbonyl functionality into the enol nonaflate intermediate followed by elimination to give the C-C triple bond. The one-pot transformations were uniformly induced by phosphazene bases combined with mildly electrophilic nonafluorobutane-1-sulfonyl fluoride.
I. M. Lyapkalo, M. A. K. Vogel, E. V. Boltukhina, J. Vavřík, Synlett, 2009, 558-561.
A SO2F2-promoted dehydration and dehydrogenation of abundant alcohols enables a direct synthesis of alkynes in high yields under mild conditions. This straightforward transformation requires only inexpensive and readily available reagents. The crude alkynes are sufficiently free of impurities to permit direct use in Cu-catalyzed alkyne-azide cycloaddition reactions with PhN3 and Sonogashira couplings.
Cyanophosphates (CPs) can be easily prepared from carbonyl compounds, and their reaction with azides provides tetrazoles. A successive termal fragmentation of the tetrazoles generates alkylidene carbenes that undergo [1,2]-rearrangement and are transformed into homologous internal and terminal alkynes in good yields under neutral conditions.
H. Yoneyama, M. Numata, K. Uemura, Y. Usami, S. Harusawa, J. Org. Chem., 2017, 82, 5538-5556.
A convenient copper-catalyzed radical reaction of readily available N-tosylhydrazones provides vinyl sulfones with excellent E stereoselectivity and broad substrate scope. An efficient one-pot synthesis of alkynes from N-tosylhydrazones has also been achieved.
S. Mao, Y.-R. Gao, X.-Q. Zhu, D.-D. Guo, Y.-Q. Wang, Org. Lett., 2015, 17, 1692-1695.
Tetra-n-butylammonium is a mild and efficient base for the elimination of bromoalkenes. Treatment of 1,1-dibromoalkenes, (Z)-1-bromoalkenes, and internal bromoalkenes with 5 equiv of TBAF • 3 H2O in DMF yielded terminal and internal alkynes in high yields without problems regarding the presence of water.
M. Okutani, Y. Mori, J. Org. Chem., 2009, 74, 442-444.
(Z)-1-Bromo-1-alkenes were stereoselectively efficiently prepared in high yields by microwave irradiation of the corresponding anti-2,3-dibromoalkanoic acids in DMF using Et3N as base. Microwave-assisted one-pot syntheses of terminal alkynes and enynes from 2,3-dibromoalkanoic acids were also developed.
C. Kuang, Q. Yang, H. Senboku, M. Tokuda, Tetrahedron, 2005, 61, 4043-4052.
(E)-α-Ethynyl-α,β-unsaturated esters were prepared in good yields from allenyl acetates by treatment with 10 mol % DABCO in DMF at room temperature.
Y. Choe, P. H. Lee, Org. Lett., 2009, 11, 1445-1448.