Categories: C-C Bond Formation > Chains >
Benzylic Substitutions, Benzylation
| Related: |
 |
 |
Recent Literature
A metal-free carbon-carbon bond-forming coupling between tosylhydrazones and
boronic acids is very general and functional-group tolerant. As the required
tosylhydrazones are easily generated from carbonyl compounds, it can be seen as
a reductive coupling of carbonyls, a process of high synthetic relevance that
requires several steps using other methodologies.
J. Barluenga, M. Tomás-Gamasa, F. Aznar, C. Valdés, Nat. Chem., 2009,
1, 494-499.
The reaction of secondary and tertiary alkyl halides with benzylic or allylic
Grignard reagents in the presence of a catalytic amount of silver nitrate in
ether yielded the corresponding cross-coupling products in high yields. The
coupling reaction provides efficient access to quaternary carbon centers.
H. Someya, H. Ohmiya, H. Yorimitsu, K. Oshima, Org. Lett., 2008,
10, 969-971.
An enantioselective nickel-catalyzed Negishi cross-coupling of racemic secondary
benzylic bromides and chlorides is described. The catalyst components are
commercially available and air-stable, and the reaction is not highly oxygen- or
moisture-sensitive.
F. O. Arp, G. C. Fu, J. Am. Chem. Soc.,
2005,
127, 10482-10483.
The use of the Xantphos ligand in a mild palladium-catalyzed Kumada-Corriu
reaction of secondary benzylic bromides with aryl and alkenyl Grignard reagents
minimizes the undesired β-elimination pathway. The corresponding cross-coupling
products can be isolated in good yields with inversion of the configuration.
A. López-Pérez, J. Adrio, J. C. Carretero, Org. Lett., 2009,
11, 5514-5517.
Alkenyltrifluoroborates can be cross-coupled
with allyl and benzyl chlorides using KOH as base in acetone-water (3:2) at 50
°C and low catalyst loadings of a 4-hydroxyacetophenone oxime derived
palladacycle giving the corresponding 1,4-dienes and allylarenes, respectively.
The use of overheated water as solvent and K2CO3 as base
allows a coupling of alkenyltrifluoroborates with aryl and heteroaryl
bromides.
E. Alacid, C. Nájera, J. Org. Chem., 2009,
74, 2321-2327.
An insoluble, amphiphilic and polymeric palladium catalyst (PdAS) is an excellent catalyst for the
Suzuki-Miyaura reaction. The catalyst is reusable after easy work up and showed
good stability in any reaction medium.
Y. M. A. Yamada, K. Takeda, H. Takashashi, S. Ikegami, J. Org. Chem.,
2003,
68, 7733-7741.
CsF with 1.1 equiv of H2O effects highly efficient
protodeboronation on tertiary diarylalkyl boronic esters with essentially
complete retention of configuration, whereas TBAFˇ3H2O can be used
for tertiary aryldialkyl boronic esters. Furthermore, substituting D2O
for H2O provides ready access to deuterium-labeled enantioenriched
tertiary alkanes. A short synthesis of the sesquiterpene (S)-turmerone is
described.
S. Nave, R. P. Sonawane, T. G. Elford, V. K. Aggarwal, J. Am. Chem. Soc., 2010,
132, 17096-17098.
Various acetals or alcohols react with allyl(trimethyl)silane or
1-phenyl-2-(trimethylsilyl)acetylene in the presence of a catalytic amount of
the Brřnsted acid o-benzenedisulfonimide under mild conditions to give
good yields of the allylated products. The catalyst can be easily recovered and
purified for use in further reactions.
M. Barbero, S. Bazzi, S. Cadamuro, S. Dughera, C. Piccinini, Synthesis, 2010,
315-319.
An enhanced Lewis acid system of InCl3 and Me3SiBr can be used to promote a
wide range of direct coupling reactions between alcohols and silyl nucleophiles
in non-halogenated solvents. Highly chemoselective allylations toward a hydroxyl
moiety over ketone and acetoxy ones have been demonstrated.
T. Saito, Y. Nishimoto, M. Yasuda, A. Baba, J. Org. Chem., 2006,
71, 8516-8522.
The reaction of alkoxides with boron trichloride results in the generation
of cations that can be allylated in subsequent transformations. The absence
of Brřnsted acids can make a significant difference in such syntheses.
G. W. Kabalka, M.-L. Yao, S. Borella, J. Am. Chem. Soc., 2006,
128, 11320-11321.
An efficient Fe(III)-catalyzed direct coupling of alkenes with alcohols and
cross-coupling of alcohols with alcohols gives the corresponding substituted (E)-alkenes
stereospecifically. Mild conditions, atom efficiency, environmental soundness,
and stereospecificity are features that make this procedure very attractive.
Additionally, this reaction could be scaled up.
Z.-Q. Liu, Y. Zhang, L. Zhao, Z. Li, J. Wang, H. Li, L.-M. Wu, Org. Lett., 2011,
13, 2208-2211.
C-O bond cleavage of lithium alkoxides occurs readily at room temperature in the
presence of titanium(IV) halides. Capture of the resultant carbocation by
alkynes provides an efficient route to trisubstituted (E)-alkenyl halides
with high stereoselectivity.
M.-L. Yao, T. R. Quick, Z. Wu, M. P. Quinn, G. W. Kabalka, Org. Lett., 2009,
11, 2647-2649.
An efficient protocol for the palladium-catalyzed Heck alkynylation using XPhos
as ligand and Cs2CO3 as the base, couples a wide range of
functionalized terminal alkynes and substituted benzyl chlorides. An excess
amount of base and higher reaction temperatures allows the synthesis of allenes
in a one-pot procedure.
C. H. Larsen, K. W. Anderson, R. E. Tundel, S. L. Buchwald, Synlett, 2006,
2941-2946.
In the presence of Pd(OAc)2 and Xphos, alkynyl carboxylic acids
smoothly underwent a decarboxylative coupling reaction with various benzyl
halides or aryl halides, providing internal alkynes in good yields. It is
noteworthy that the optimal conditions are compatible with a wide range of aryl
halides.
W.-W. Zhang, X.-G. Zhang, J.-H. Li, J. Org. Chem., 2010,
75, 5259-5264.
The reaction of alkynylboron dihalides with benzylic, allylic, and
propargylic alcohols provides an efficient route to internal acetylenes
without isomerization of the product alkynes under the reaction conditions.
G. W. Kabalka, M.-L. Yao, S. Borella, Org. Lett.,
2006,
8, 879-881.
A nickel-catalyzed reductive carboxylation of styrenes using CO2
proceeds under mild conditions using diethylzinc as the reductant. The catalyst
system is very robust and will fixate CO2 in good yield even if
exposed to only an equimolar amount introduced into the headspace above the
reaction.
C. M. Williams, J. B. Johnson, T. Rovis, J. Am. Chem. Soc., 2008,
130, 14936-14937.
Transition metal carbenes can directly be generated from readily available and
stable 1-sulfonyl-1,2,3-triazoles in the presence of chiral Rh(II) carboxylates
and can be used in a highly efficient enantioselective C-H insertion of azavinyl
carbenes into unactivated alkanes to access various β-chiral sulfonamides.
S. Chuprakov, J. A. Malik, M. Zibinsky, V. V. Fokin, J. Am. Chem. Soc., 2011,
133, 10352-10355.
