Transition Metal–
Mediated Alkenylations,
Arylations, and
13
Alkynylations
As a rule, halogens, OH groups, and all other O substituents that are attached to
A
an sp2-hybridized C atom of an alkene or an aromatic compound cannot be
substituted by nucleophiles alone. One exception has already been discussed and
that was the addition/elimination mechanism of the nucleophilic substitution.
This mechanism oc- curs, among other substrates, with alkenes that carry a strong
electron acceptor on the neighboring C atom (see Figures 8.36–8.38 for examples).
The same mechanism is known to also operate for aromatic compounds—under
the condition, again, that they carry an acceptor substituent at an appropriate
position (Section 5.5). The benzyne mechanism of nucleophilic substitution, that
is, an elimination/addition mechanism (Section 5.6), presents a second mode of
nucleophilic substitution of a halogen at an sp2-hybridized C atom.
Halogens or O-bound leaving groups, however, also can be detached from the
sp2- hybridized C atom of an alkene or an aromatic compound
• if organometallic compounds act as nucleophiles, and
• if a transition metal is present in at least catalytic amounts. These SN reactions
are designated as C,C-coupling reactions.
The most important substrates for substitutions of this type are alkenyl and aryl
tri- flates, bromides, or iodides (Sections 13.1–13.3). The most important
organometallic compounds to be introduced into the substrates contain Cu, Mg, B,
or Zn. The metal- bound C atom can be sp3-, sp2-, or sp-hybridized in these
compounds, and each of these species, in principle, is capable of attacking
unsaturated substrates. Organocopper com- pounds most usually (Section 13.1), but
not always (Section 13.3.4), substitute without the need for a catalyst. Grignard
compounds substitute in the presence of catalytic amounts of Ni complexes
(Section 13.2), while organoboron (Section 13.3.2) and organozinc (Section
13.3.3) compounds typically are reacted in the presence of Pd(PPh3)4.
All these C,C-coupling reactions can be carried out in an analogous fashion at sp-
hybridized carbons, too, as long as this carbon binds to a Br or I as a leaving group.
However, we will present this type of reaction only briefly, in Section 13.4.
In Section 13.5, a few other C,C-coupling reactions of alkenes and of aromatic
com- pounds, which contain an sp2¬OTf, an sp2¬Br, or an sp2¬Cl bond, will be
discussed because these C,C couplings and the preceding ones are closely related
,mechanisti- cally. These substrates, however, react with metal-free alkenes.
Palladium-complexes again serve as the catalysts.
,520 13 Transition Metal–Mediated Alkenylations, Arylations, and Alkynylations
13.1 Alkenylation and Arylation
of Copper-Bound Organyl
Groups
Me2CuLi couples with a variety of alkenyl triflates (bromides, iodides) giving methyl
derivatives (Table 13.1), and, in complete analogy, with aryl triflates (bromides,
iodides) giving toluenes.
Table 13.1. Product Spectrum of C,C-Coupling Reactions with Me2CuLi
OSO2CF3
ArOSO2CF3
Me Br (I) R or
Substrate R
Br (I) Ar I(Br)
Preparation Fig. 13.10 i.e., as in
according to ... Fig. 10.20 Fig. 13.10 Fig. 13.12 Section 5.2.1
Me
Reaction with Me Me R
Me2CuLi yields R Ar Me
Me
In reactions of alkenyl triflates with stereogenic C“C double bonds, coupling reac-
tions of these kinds convert the Csp2¬X bond of the alkenyl triflate into the
Csp2¬C bond of the substitution product with complete retention of configuration.
The stereo- selective synthesis of a 1,3-diene from an alkenyl triflate and
(vinyl)2CuLi provides an example (Figure 13.1).
Gilman cuprates also convert the Csp2¬Br and Csp2¬I bonds of stereogenic haloal-
kenes into a Csp2¬C bond with complete retention of configuration (Table
13.1,
triflate bond is converted into the C sp2¬C bond 1) LDA, THF, –
O
of the product with complete retention of 78 C
(regarding the
configuration. stereoselectivity, compare
the
discussion of Fig. 10.12,
Fig. 13.1. Stereoselective but not Fig. 10.12 itself)
synthesis of a PhN(SO2CF3)2
(see Fig. 10.20 about the
trisubstituted ethylene by
method)
way of C,C coupling of a
Gilman reagent. The C sp2–
, O SO2CF3
CuLi
2
Mediated Alkenylations,
Arylations, and
13
Alkynylations
As a rule, halogens, OH groups, and all other O substituents that are attached to
A
an sp2-hybridized C atom of an alkene or an aromatic compound cannot be
substituted by nucleophiles alone. One exception has already been discussed and
that was the addition/elimination mechanism of the nucleophilic substitution.
This mechanism oc- curs, among other substrates, with alkenes that carry a strong
electron acceptor on the neighboring C atom (see Figures 8.36–8.38 for examples).
The same mechanism is known to also operate for aromatic compounds—under
the condition, again, that they carry an acceptor substituent at an appropriate
position (Section 5.5). The benzyne mechanism of nucleophilic substitution, that
is, an elimination/addition mechanism (Section 5.6), presents a second mode of
nucleophilic substitution of a halogen at an sp2-hybridized C atom.
Halogens or O-bound leaving groups, however, also can be detached from the
sp2- hybridized C atom of an alkene or an aromatic compound
• if organometallic compounds act as nucleophiles, and
• if a transition metal is present in at least catalytic amounts. These SN reactions
are designated as C,C-coupling reactions.
The most important substrates for substitutions of this type are alkenyl and aryl
tri- flates, bromides, or iodides (Sections 13.1–13.3). The most important
organometallic compounds to be introduced into the substrates contain Cu, Mg, B,
or Zn. The metal- bound C atom can be sp3-, sp2-, or sp-hybridized in these
compounds, and each of these species, in principle, is capable of attacking
unsaturated substrates. Organocopper com- pounds most usually (Section 13.1), but
not always (Section 13.3.4), substitute without the need for a catalyst. Grignard
compounds substitute in the presence of catalytic amounts of Ni complexes
(Section 13.2), while organoboron (Section 13.3.2) and organozinc (Section
13.3.3) compounds typically are reacted in the presence of Pd(PPh3)4.
All these C,C-coupling reactions can be carried out in an analogous fashion at sp-
hybridized carbons, too, as long as this carbon binds to a Br or I as a leaving group.
However, we will present this type of reaction only briefly, in Section 13.4.
In Section 13.5, a few other C,C-coupling reactions of alkenes and of aromatic
com- pounds, which contain an sp2¬OTf, an sp2¬Br, or an sp2¬Cl bond, will be
discussed because these C,C couplings and the preceding ones are closely related
,mechanisti- cally. These substrates, however, react with metal-free alkenes.
Palladium-complexes again serve as the catalysts.
,520 13 Transition Metal–Mediated Alkenylations, Arylations, and Alkynylations
13.1 Alkenylation and Arylation
of Copper-Bound Organyl
Groups
Me2CuLi couples with a variety of alkenyl triflates (bromides, iodides) giving methyl
derivatives (Table 13.1), and, in complete analogy, with aryl triflates (bromides,
iodides) giving toluenes.
Table 13.1. Product Spectrum of C,C-Coupling Reactions with Me2CuLi
OSO2CF3
ArOSO2CF3
Me Br (I) R or
Substrate R
Br (I) Ar I(Br)
Preparation Fig. 13.10 i.e., as in
according to ... Fig. 10.20 Fig. 13.10 Fig. 13.12 Section 5.2.1
Me
Reaction with Me Me R
Me2CuLi yields R Ar Me
Me
In reactions of alkenyl triflates with stereogenic C“C double bonds, coupling reac-
tions of these kinds convert the Csp2¬X bond of the alkenyl triflate into the
Csp2¬C bond of the substitution product with complete retention of configuration.
The stereo- selective synthesis of a 1,3-diene from an alkenyl triflate and
(vinyl)2CuLi provides an example (Figure 13.1).
Gilman cuprates also convert the Csp2¬Br and Csp2¬I bonds of stereogenic haloal-
kenes into a Csp2¬C bond with complete retention of configuration (Table
13.1,
triflate bond is converted into the C sp2¬C bond 1) LDA, THF, –
O
of the product with complete retention of 78 C
(regarding the
configuration. stereoselectivity, compare
the
discussion of Fig. 10.12,
Fig. 13.1. Stereoselective but not Fig. 10.12 itself)
synthesis of a PhN(SO2CF3)2
(see Fig. 10.20 about the
trisubstituted ethylene by
method)
way of C,C coupling of a
Gilman reagent. The C sp2–
, O SO2CF3
CuLi
2
