Abstract:The pyrrolidine (6) obtained in experiment 2 could be prepared, in 90% yield, also by treatment of one mol of the azomethine N-benzylidenebenzylamine in THF at 20°C with one mol of 2-methylbutadiene and a catalytic amount (0.05 mol) of lithium pyrrolidide. Apparently the lithium pyrrolidide formed in the addition process is able to metalate the azomethine smoothly. This base-catalyzed union of an azomethine (10) and an alkene, which is presumably not restricted to the special system discussed here, may lead to… Show more
“…To the best of our knowledge this represents the only example of a 2-azaallyllithium species undergoing such a reaction. Prior to our work, only acyclic aryl-stabilized 2-azaallyllithium species were investigated with 1,3-dienes producing mainly [π4s+π2s] cycloadducts. , …”
Section: Resultsmentioning
confidence: 99%
“…The limitations outlined above have precluded the routine use of 1,3-dipoles in higher order cycloadditions in total syntheses. Moreover, allylic anions have been shown to participate in higher order [π6s+π4s] reactions with conjugated polyenes while the isoelectronic aryl-stabilized 2-azaallyl anions were found to participate predominantly in [π4s+π2s] cycloadditions …”
2-Azaallyllithium species [R(1)CH(-)N=C(X)R(2)Li(+), where R(1) and R(2) are alkyl and X = OMe] were generated by tin-lithium exchange of (2-azaallyl)stannanes and underwent [pi4s+pi2s] and [pi6s+pi4s] cycloadditions with cyclic dienes and trienes, respectively, to generate novel bridged azabicyclic compounds in a highly diastereoselective endo fashion. The periselectivity using cycloheptatriene was modest, producing a 1:1 mixture of [pi6s+pi4s] and [pi4s+pi2s] adducts. The reactions of 2-azaallyllithium species with dienes proceeded by a [pi4s+pi2s] pathway. The cycloadducts derived from cyclic 2-azaallyllithium species possess the 7-azabicyclo[2.2.1]heptane (tropane) or 8-azabicyclo[3.2.1]octane ring system and have been elaborated into cocaine-like analogues.
“…To the best of our knowledge this represents the only example of a 2-azaallyllithium species undergoing such a reaction. Prior to our work, only acyclic aryl-stabilized 2-azaallyllithium species were investigated with 1,3-dienes producing mainly [π4s+π2s] cycloadducts. , …”
Section: Resultsmentioning
confidence: 99%
“…The limitations outlined above have precluded the routine use of 1,3-dipoles in higher order cycloadditions in total syntheses. Moreover, allylic anions have been shown to participate in higher order [π6s+π4s] reactions with conjugated polyenes while the isoelectronic aryl-stabilized 2-azaallyl anions were found to participate predominantly in [π4s+π2s] cycloadditions …”
2-Azaallyllithium species [R(1)CH(-)N=C(X)R(2)Li(+), where R(1) and R(2) are alkyl and X = OMe] were generated by tin-lithium exchange of (2-azaallyl)stannanes and underwent [pi4s+pi2s] and [pi6s+pi4s] cycloadditions with cyclic dienes and trienes, respectively, to generate novel bridged azabicyclic compounds in a highly diastereoselective endo fashion. The periselectivity using cycloheptatriene was modest, producing a 1:1 mixture of [pi6s+pi4s] and [pi4s+pi2s] adducts. The reactions of 2-azaallyllithium species with dienes proceeded by a [pi4s+pi2s] pathway. The cycloadducts derived from cyclic 2-azaallyllithium species possess the 7-azabicyclo[2.2.1]heptane (tropane) or 8-azabicyclo[3.2.1]octane ring system and have been elaborated into cocaine-like analogues.
“…A CT structure in a low molecular weight compound, 2-(2‘-thienyl)pyridine (ThPy), which corresponds to the repeating unit of PThPy, has been proposed on the basis of its chemical reactivity …”
Section: Optical and Electrical Propertiesmentioning
Various π-conjugated copolymers constituted of π-excessive
thiophene, selenophene, or furan units
(Ar) and π-deficient pyridine or quinoxaline (Ar‘) units have been
prepared in high yields by the following
organometallic polycondensation methods: (i) n
X−Ar−Ar‘−X + n Ni(0)Lm →
(-Ar−Ar‘)-
n
(X = halogen, Ni(0)Lm = zerovalent nickel complex), (ii) n X−Ar−X +
n Me3Sn−Ar‘−SnMe3 →
(-Ar−Ar‘)-
n
(palladium catalyzed),
and (iii) a X−Ar−X + b X−Ar‘−X +
(a + b)Ni(0)Lm →
(-Ar)
x
(Ar‘)-
y
.
Powder X-ray diffraction analysis confirms
an alternative structure of a polymer prepared by the method ii.
The copolymers have a molecular weight of 5.4 ×
103 to 3.3 × 105 and an [η] value of 0.37
to 4.4 dL g-1. π−π* absorption bands of the
copolymers generally show
red shifts from those of the corresponding homopolymers,
(-Ar)-
n
and
(-Ar‘)-
n
,
and the red shifts are accounted for by
charge-transferred CT structures of the copolymers. For example,
an alternative copolymer of thiophene and 2,3-diphenylquinoxaline gives rise to an absorption band at
λmax = 603 nm, whereas homopolymers of thiophene
and
2,3-diphenylquinoxaline exhibit absorption peaks at about 460 and 440
nm, respectively. The CT copolymers are
electrochemically active in both oxidation and reduction regions,
showing oxidation (or p-doping) peaks in a range
of 0.39 to 1.32 V vs Ag/Ag+ and reduction (or
n-doping) peaks in a range of −1.80 to −2.22 V vs
Ag/Ag+,
respectively. Copolymers of pyridine give unique cyclic
voltammograms exhibiting p-undoping peaks at potentials
much different (about 2−3 V lower) from the corresponding p-doping
potentials, and this large difference between
p-doping and p-undoping potentials is explained by an EC mechanism.
They are converted into semiconductors by
chemical and electrochemical oxidation and reduction. Copolymers
of thiophene with pyridine and quinoxaline
show the third-order nonlinear optical susceptibility
χ(3) of about 5 × 10-11 esu at the
three-photon resonant wavelength,
which is 5−7 times larger than those of the corresponding
homopolymers and related to the CT structure in the
copolymers.
Carbon‐carbon sigma‐bond formation one of the most fundamental operations in organic chemistry, is often accomplished by interaction of an organometallic reagent with an organic substrate having a suitable leaving group. Selective substitution of halogens and of alcohol derivatives by various hydrocarbon groups in many different types of organic substrates has been achieved most successfully using organocopper reagents. The wide scope and effectiveness of these reagents in coupling with halides and alcohol derivatives have made formation of the unsymmetrical coupling product R‐R' a useful reaction in organic synthesis, allowing efficient and specific substitution of X by alkyl, alkenyl, alkynyl, or aryl groups. Because selective coupling between organic substrate and organocopper reagent is usually achieved more effectively by stoichiometric than by catalytic organocopper reagents, and more effectively still by organocuprates(I) than by mono‐copper or by complexed organocopper reagents, the emphasis in this chapter is on organocuprates (I). Consideration is given to possible mechanisms of substitution reactions using organocopper reagents, to scope, limitations, and synthetic utility of these reactions, and to optimal experimental considerations for their application.
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