28 research outputs found
A Light-Induced Vinylogous Nazarov-Type Cyclization
The first examples
of a photochemically induced vinylogous Nazarov-type
cyclization forming a cycloheptadienone core are described. The reaction
can be included in a three-step cascade consisting of a photochemical
isoxazole–azirine ring contraction, cobaltÂ(II)-catalyzed ring
expansion, and the photochemical cyclization. Furthermore, the first
representative of the hitherto unknown 1-azatricycloÂ[2.2.0.0<sup>2,6</sup>]Âhexanes has been identified as a side product of
the azirine formation
A Light-Induced Vinylogous Nazarov-Type Cyclization
The first examples
of a photochemically induced vinylogous Nazarov-type
cyclization forming a cycloheptadienone core are described. The reaction
can be included in a three-step cascade consisting of a photochemical
isoxazole–azirine ring contraction, cobaltÂ(II)-catalyzed ring
expansion, and the photochemical cyclization. Furthermore, the first
representative of the hitherto unknown 1-azatricycloÂ[2.2.0.0<sup>2,6</sup>]Âhexanes has been identified as a side product of
the azirine formation
Intramolecularly Coordinated Bis(crown ether)-Substituted Organotin Halides as Ditopic Salt Receptors
The
synthesis of the bisÂ(crown ether)-substituted organostannanes
X<sub>2</sub>SnÂ(CH<sub>2</sub>-[16]-crown-5)<sub>2</sub> (<b>3</b>, X = I; <b>4</b>, X = Br; <b>5</b>, X = Cl; <b>6</b>, X = F) and X<sub>2</sub>SnÂ(CH<sub>2</sub>-[13]-crown-4)<sub>2</sub> (<b>10</b>, X = I; <b>11</b>, X = Br; <b>12</b>, X = F) is reported. The compounds have been characterized by <sup>1</sup>H, <sup>13</sup>C, <sup>19</sup>F, and <sup>119</sup>Sn NMR
spectroscopy, elemental
analyses, and electrospray ionization mass spectrometry (ESI-MS).
Single-crystal X-ray diffraction analyses reveal a distorted-octahedral <i>cis</i>,<i>cis</i>,<i>trans </i>configuration
of the tin atoms in compounds <b>4</b>–<b>6</b> and <b>10</b>–<b>12</b> as a result of intramolecular
O→Sn coordination. The ability of the host molecules to form
mono- and ditopic complexes with various halide salts in different
solvents, including water, has been investigated by NMR spectroscopy
and ESI-MS
Cyclic Dinuclear Organotin Cations Stabilized by Bulky Substituents
The
syntheses of sterically congested 2,2-bisÂ(diorganochloridostannyl)Âpropane,
Me<sub>2</sub>CÂ(SnClR<sub>2</sub>)<sub>2</sub> (<b>1</b>; R
= CHÂ(SiMe<sub>3</sub>)<sub>2</sub>), the related salts [cyclo-{Me<sub>2</sub>CÂ(SnR<sub>2</sub>)<sub>2</sub>X}ÂBÂ(Ar<sup>F</sup>)<sub>4</sub>] (<b>2</b>, X = Cl; <b>3</b>, X = OAc; <b>4</b>, X = OH; Ar<sup>F</sup> = 3,5-(CF<sub>3</sub>)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>), and the four-membered-ring cyclo-{Me<sub>2</sub>CÂ(SnR<sub>2</sub>)<sub>2</sub>O} (<b>5</b>) are reported. The
compounds have been characterized by elemental and EDX analyses, <sup>1</sup>H, <sup>11</sup>B, <sup>13</sup>C, <sup>19</sup>F, <sup>29</sup>Si, and <sup>119</sup>Sn NMR and IR spectroscopy, electrospray ionization
mass spectrometry, and single-crystal X-ray diffraction analysis
Novel Stannatrane N(CH<sub>2</sub>CMe<sub>2</sub>O)<sub>2</sub>(CMe<sub>2</sub>CH<sub>2</sub>O)SnO-<i>t-</i>Bu and Related Oligonuclear Tin(IV) Oxoclusters. Two Isomers in One Crystal
The syntheses of
the alkanolamine NÂ(CH<sub>2</sub>CMe<sub>2</sub>OH)<sub>2</sub>(CMe<sub>2</sub>CH<sub>2</sub>OH) (<b>1</b>), of the stannatrane NÂ(CH<sub>2</sub>CMe<sub>2</sub>O)<sub>2</sub>(CMe<sub>2</sub>CH<sub>2</sub>O)ÂSnO-<i>t-</i>Bu (<b>2</b>), and of the trinuclear
tin oxocluster <b>3</b> consisting of the two isomers [(ÎĽ<sub>3</sub>-O)Â(O-<i>t</i>-Bu)Â{SnÂ(OCH<sub>2</sub>CMe<sub>2</sub>)Â(OCMe<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>N}<sub>3</sub>] (<b>3a</b>) and [(ÎĽ<sub>3</sub>-O)Â(ÎĽ<sub>3</sub>-O-<i>t</i>-Bu)Â{SnÂ(OCH<sub>2</sub>CMe<sub>2</sub>)Â(OCMe<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>N}<sub>3</sub>] (<b>3b</b>) as well
as the isolation of a few crystals of the hexanuclear tin oxocluster
[LSnOSnÂ(OH)<sub>3</sub>LSnOH]<sub>2</sub> [L = NÂ(CH<sub>2</sub>CMe<sub>2</sub>O)<sub>2</sub>(CMe<sub>2</sub>CH<sub>2</sub>O)] (<b>4</b>) are reported. The compounds were characterized by <sup>1</sup>H, <sup>13</sup>C, <sup>15</sup>N, and <sup>119</sup>Sn (<b>1–3</b>) nuclear magnetic resonance and infrared spectroscopy, electrospray
ionization mass spectrometry, and single-crystal X-ray diffraction
analysis (<b>1–4</b>). A graph set analysis was performed
for compound <b>1</b>. The relative energies of <b>3a</b> and <b>3b</b> were estimated by density functional theory
calculations that show that the energy differences are small
Iodocyclization of <i>o</i>‑Alkynylbenzamides Revisited: Formation of Isobenzofuran-1(3<i>H</i>)‑imines and 1<i>H</i>‑Isochromen-1-imines Instead of Lactams
The iodocyclization of <i>o</i>-alkynylbenzamides
with
various electrophiles has been reported to yield five- or six-membered
lactams by nucleophilic attack of the amide nitrogen onto the triple
bond. While the formation of an isobenzofuran-1Â(3<i>H</i>)-imine with two bulky substituents under Larock conditions was initially
attributed to steric hindrance, we found out that cyclization via
the amide oxygen is the rule rather than the exception. Thus, the
structures of the products reported in the literature need to be revised
Iodocyclization of <i>o</i>‑Alkynylbenzamides Revisited: Formation of Isobenzofuran-1(3<i>H</i>)‑imines and 1<i>H</i>‑Isochromen-1-imines Instead of Lactams
The iodocyclization of <i>o</i>-alkynylbenzamides
with
various electrophiles has been reported to yield five- or six-membered
lactams by nucleophilic attack of the amide nitrogen onto the triple
bond. While the formation of an isobenzofuran-1Â(3<i>H</i>)-imine with two bulky substituents under Larock conditions was initially
attributed to steric hindrance, we found out that cyclization via
the amide oxygen is the rule rather than the exception. Thus, the
structures of the products reported in the literature need to be revised
Iodocyclization of <i>o</i>‑Alkynylbenzamides Revisited: Formation of Isobenzofuran-1(3<i>H</i>)‑imines and 1<i>H</i>‑Isochromen-1-imines Instead of Lactams
The iodocyclization of <i>o</i>-alkynylbenzamides
with
various electrophiles has been reported to yield five- or six-membered
lactams by nucleophilic attack of the amide nitrogen onto the triple
bond. While the formation of an isobenzofuran-1Â(3<i>H</i>)-imine with two bulky substituents under Larock conditions was initially
attributed to steric hindrance, we found out that cyclization via
the amide oxygen is the rule rather than the exception. Thus, the
structures of the products reported in the literature need to be revised
Iodocyclization of <i>o</i>‑Alkynylbenzamides Revisited: Formation of Isobenzofuran-1(3<i>H</i>)‑imines and 1<i>H</i>‑Isochromen-1-imines Instead of Lactams
The iodocyclization of <i>o</i>-alkynylbenzamides
with
various electrophiles has been reported to yield five- or six-membered
lactams by nucleophilic attack of the amide nitrogen onto the triple
bond. While the formation of an isobenzofuran-1Â(3<i>H</i>)-imine with two bulky substituents under Larock conditions was initially
attributed to steric hindrance, we found out that cyclization via
the amide oxygen is the rule rather than the exception. Thus, the
structures of the products reported in the literature need to be revised
Iodocyclization of <i>o</i>‑Alkynylbenzamides Revisited: Formation of Isobenzofuran-1(3<i>H</i>)‑imines and 1<i>H</i>‑Isochromen-1-imines Instead of Lactams
The iodocyclization of <i>o</i>-alkynylbenzamides
with
various electrophiles has been reported to yield five- or six-membered
lactams by nucleophilic attack of the amide nitrogen onto the triple
bond. While the formation of an isobenzofuran-1Â(3<i>H</i>)-imine with two bulky substituents under Larock conditions was initially
attributed to steric hindrance, we found out that cyclization via
the amide oxygen is the rule rather than the exception. Thus, the
structures of the products reported in the literature need to be revised