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Synthesis of terminal olefins
More general methods can be found here.
1-methyl-2-(methylsulfonyl)benzimidazole reacts with a variety of aldehydes and ketones in the presence of either NaHMDS (-55 ░C to rt) or t-BuOK (rt, 1 h) in DMF to give the corresponding terminal alkenes in high yields. The byproducts of this Julia-type methylenation reagent are easily removed, and the reaction conditions are mild and practical.
K. Ando, T. Kobayashi, N. Uchida, Org. Lett., 2015, 17, 2554-2557.
The methylenation of aldehydes and ketones under optimized Julia-Kocienski conditions was conducted by using 1-tert-butyl-1H-tetrazol-5-ylmethyl sulfone with either NaHMDS at -78░C or Cs2CO3 at 70░C. The latter conditions are also adapted for the preparation of 1,2-disubstituted olefins and intramolecular olefinations.
C. A´ssa, J. Org. Chem., 2006, 71, 360-363.
Inexpensive (NHC)-Cu complexes efficiently catalyzed the methylenation of various aliphatic and aromatic carbonyl compounds in the presence of trimethylsilyldiazomethane, triphenylphosphine, and 2-propanol. High yields were obtained for the formation of styrenes containing nitro, trifluoromethyl, amino, and ester groups.
H. Lebel, M. Davi, S. DÝez-Gonzlez, S. P. Nolan, J. Org. Chem., 2007, 72, 144-149.
A mild and nonbasic rhodium-catalyzed methylenation of aldehydes using trimethylsilyldiazomethane and triphenylphosphine in THF produces various terminal alkenes in excellent yields including enolizable keto aldehydes and nonracemic aldehydes. The use of an easily removable phosphine is also described.
H. Lebel, V. Paquet, J. Am. Chem. Soc., 2004, 126, 320-328.
A mechanistically distinct tactic to carry E2-type eliminations on alkyl halides is based on the interplay of α-aminoalkyl radical-mediated halogen-atom transfer (XAT) with desaturative cobalt catalysis. The methodology is high-yielding and tolerates many functionalities. Fine-tuning of the electronic and steric properties of the cobalt catalyst provides high olefin positional selectivity.
H. Zhao, A. J. McMillan, T. Constantin, R. C. Mykura, F. Juliß, D. Leonori, J. Am. Chem. Soc., 2021, 143, 14646-14656.
The bidentate phosphine DPPM mediates an efficient methylenation of acyl fluorides and acyl chlorides substituted with aryl, alkenyl, and alkyl groups with trimethylaluminum to provide various 2-substituted propene derivatives.
X. Wang, Z. Wang, Y. Asanuma, Y. Nishihara, Org. Lett., 2019, 21, 3640-3643.
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.
A transformation of aldehydes into terminal olefins through reduction of the corresponding enol triflates is effective with both linear and α-branched aldehydes.
S. K. Pandey, A. E. Greene, J.-F. Poisson, J. Org. Chem., 2007, 72, 7769-7770.
A stepwise PCET activation of thermodynamically stable olefins is mediated by an excited-state oxidant and a Br°nsted base to afford an allylic radical that is captured by a Cr(II) cocatalyst to furnish an allylchromium(III) intermediate. In situ protodemetalation of this allylchromium complex by methanol is highly regioselective and affords an isomerized and less thermodynamically stable alkene product.
K. Zhao, R. R. Knowles, J. Am. Chem. Soc., 2022, 144, 137-144.
β-Hydride elimination, an undesired elementary step in palladium-catalyzed cross-coupling reactions, allows dehydrohalogenations of alkyl bromides to form terminal olefins in excellent yield at room temperature in the presence of various functional groups.
A. C. Bissember, A. Levina, G. C. Fu, J. Am. Chem. Soc., 2012, 134, 14232-14237.
Heating with NaI and DBU in dimethoxyethane effected clean elimination of tosylates to terminal olefins. This simple one-pot procedure was also applied to tosylates derived from an Evans Aldol Reaction.
P. Phukan, M. Bauer, M. E. Maier, Synthesis, 2003, 1324-1328.
The preparation of any length alkenyl halide from inexpensive starting reagents is reported. Standard organic transformations were used to prepare straight chain α-olefin halides in excellent overall yields with no detectable olefin isomerization and full recovery of any unreacted starting material.
T. W. Baughman, J. C. Sworen, K. B. Wagener, Tetrahedron, 2004, 60, 10943-10948.
A Rh-catalyzed dehomologation of primary alcohols enables the synthesis of olefins via an oxidation-dehydroformylation sequence in the presence of N,N-dimethylacrylamide as hydrogen acceptor. Alcohols with diverse functionality and structure undergo oxidative dehydroxymethylation to access the corresponding olefins.
X. Wu, F. A. Cruz, A. Lu, V. M. Dong, J. Am. Chem. Soc., 2018, 140, 10126-10130.
In the presence of a 1:1 mixture of n-butyllithium and lithioacetonitrile in THF, a series of styrene oxides can be converted into one-carbon homologated allyl alcohols in an unusual regioselective manner.
T. Tomioka, R. Sankranti, T. Yamada, C. Clark, Org. Lett., 2013, 15, 5099-5101.
Two optimal catalytic systems for the convenient and fast α-methylenation of aldehydes with aqueous formaldehyde are described that allow short reaction times and afford the methylenated products in good to excellent yields and chemoselectivity.
A. Erkkilń, P. M. Pihko, J. Org. Chem., 2006, 71, 2538-2541.
Regioselective C-C bond fragmentation of cyclopropanes followed by desulfonylation enables a one-step strategy for the synthesis of α-methenyl ketones from β-keto sufones. Success of the methodology is elaborated for the synthesis of chromanones and isoflavanones in one-step.
G. Pandey, J. Vaitla, Org. Lett., 2015, 17, 4890-4893.
The application of the 1-butyl-3-methylimidazolium-based ionic liquid [BMIM][NTf2] as solvent enabled clean α-methylenations of carbonyl compounds in a short time and good yields. This ionic liquid was reused without affecting the reaction rates or yields over seven runs.
J. A. Vale, D. F. Zanchetta, P. J. S. Moran, J. A. R. Rodrigues, Synlett, 2009, 75-78.
Various aryl ketone derivatives react readily with DMSO under transition metal-free reaction condition, producing the α,β-unsaturated carbonyl compounds in good yields. This direct α-Csp3-H methylenation offers wide substrate scope and provides an efficient and expeditious approach to an important class of α,β-unsaturated carbonyl compounds.
Y.-F. Liu, P. Yi Ji, J.-W. Xu, Y.-Q. Hu, Q. Liu, W.-P. Luo, C.-C. Guo, J. Org. Chem., 2017, 82, 7161-7164.
Gold catalysis enables a chemoselective α-methylenation of aromatic ketones using Selectfluor as a methylenating agent to provide various 1,2-disubstituted propenone derivatives in good yields. This reaction offers simple operation, good functional group tolerance, and broad scope of substrates.
H. Zhu, X. Meng, Y. Zhang, G. Chen, Z. Cao, X. Sun, J. You, J. Org. Chem., 2017, 82, 12059-12065.
An expeditious synthesis of α-substituted tert-butyl acrylates from commercially available aldehydes and Meldrum's acid includes a telescoped condensation-reduction sequence to afford 5-monosubstituted Meldrum's acid derivatives followed by a Mannich-type reaction triggered by a rapid cycloreversion of the dioxinone ring on heating with tert-butyl alcohol.
C. G. Frost, S. D. Penrose, R. Gleave, Synthesis, 2009, 627-635.