Strained cyclic allenes, first discovered in 1966 by Wittig and co‐workers, have recently emerged as valuable synthetic building blocks. Previous experimental investigations, and computations reported here, demonstrate that the Diels–Alder reactions of furans and pyrroles with 1,2‐cyclohexadiene and oxa‐ and azaheterocyclic analogs proceed with
Strained cyclic allenes, first discovered in 1966 by Wittig and co‐workers, have recently emerged as valuable synthetic building blocks. Previous experimental investigations, and computations reported here, demonstrate that the Diels–Alder reactions of furans and pyrroles with 1,2‐cyclohexadiene and oxa‐ and azaheterocyclic analogs proceed with
- NSF-PAR ID:
- 10232273
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 27
- ISSN:
- 1433-7851
- Format(s):
- Medium: X Size: p. 14989-14997
- Size(s):
- ["p. 14989-14997"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract endo selectivity. Thisendo selectivity gives the adduct with the allylic saturated carbon of the cyclic alleneendo to the diene carbons. The selectivity is very general and useful in synthetic applications. Our computational study establishes the origins of thisendo selectivity. We analyze the helical frontier molecular orbitals of strained cyclic allenes and show how secondary orbital and electrostatic effects influence stereoselectivity. The LUMO of carbon‐3 of the allene (C‐3 is not involved in primary orbital interactions) interacts in a stabilizing fashion with the HOMO of the diene in such a way that the carbon of the cyclic allene attached to C‐1 favors theendo position in the transition state. The furan LUMO, allene HOMO interaction reinforces this preference. These mechanistic studies are expected to prompt the further use of long‐avoided strained cyclic allenes in chemical synthesis. -
Abstract The chemistry of strained cyclic alkynes has undergone a renaissance over the past two decades. However, a related species, strained cyclic allenes, especially heterocyclic derivatives, have only recently resurfaced and represent another class of valuable intermediates. We report a mild and facile means to generate the parent 3,4‐oxacyclic allene from a readily accessible silyl triflate precursor, and then trap it in (4+2), (3+2), and (2+2) reactions to provide a variety of cycloadducts. In addition, we describe a catalytic, decarboxylative asymmetric allylic alkylation performed on an α‐silylated substrate, to ultimately permit access to an enantioenriched allene. Generation and trapping of the enantioenriched cyclic allene occurs with complete transfer of stereochemical information in a Diels–Alder cycloaddition through a point‐chirality, axial‐chirality, point‐chirality transfer process.
-
Abstract The chemistry of strained cyclic alkynes has undergone a renaissance over the past two decades. However, a related species, strained cyclic allenes, especially heterocyclic derivatives, have only recently resurfaced and represent another class of valuable intermediates. We report a mild and facile means to generate the parent 3,4‐oxacyclic allene from a readily accessible silyl triflate precursor, and then trap it in (4+2), (3+2), and (2+2) reactions to provide a variety of cycloadducts. In addition, we describe a catalytic, decarboxylative asymmetric allylic alkylation performed on an α‐silylated substrate, to ultimately permit access to an enantioenriched allene. Generation and trapping of the enantioenriched cyclic allene occurs with complete transfer of stereochemical information in a Diels–Alder cycloaddition through a point‐chirality, axial‐chirality, point‐chirality transfer process.
-
Abstract The mechanism of the intermolecular hydroamination of 3‐methylbuta‐1,2‐diene (
1 ) withN ‐methylaniline (2 ) catalyzed by (IPr)AuOTf has been studied by employing a combination of kinetic analysis, deuterium labelling studies, and in situ spectral analysis of catalytically active mixtures. The results of these and additional experiments are consistent with a mechanism for hydroamination involving reversible, endergonic displacement ofN ‐methylaniline from [(IPr)Au(NHMePh)]+(4 ) by allene to form the cationic gold π‐C1,C2 ‐allene complex [(IPr)Au(η2‐H2C=C=CMe2)]+(I ), which is in rapid, endergonic equilibrium with the regioisomeric π‐C2,C3 ‐allene complex [(IPr)Au(η2‐Me2C=C=CH2)]+(I′ ). Rapid and reversible outer‐sphere addition of2 to the terminal allene carbon atom ofI′ to form gold vinyl complex (IPr)Au[C(=CH2)CMe2NMePh] (II ) is superimposed on the slower addition of2 to the terminal allene carbon atom ofI to form gold vinyl complex (IPr)Au[C(=CMe2)CH2NMePh] (III ). Selective protodeauration ofIII releasesN ‐methyl‐N ‐(3‐methylbut‐2‐en‐1‐yl)aniline (3 a ) with regeneration of4 . At high conversion, gold vinyl complexII is competitively trapped by an (IPr)Au+fragment to form the cationic bis(gold) vinyl complex {[(IPr)Au]2[C(=CH2)CMe2NMePh]}+(6 ). -
Abstract ipso ‐Arylative ring‐opening polymerization of 2‐bromo‐8‐aryl‐8H ‐indeno[2,1‐b]thiophen‐8‐ol monomers proceeds to Mnup to 9 kg mol−1with conversion of the monomer diarylcarbinol groups to pendent conjugated aroylphenyl side chains (2‐benzoylphenyl or 2‐(4‐hexylbenzoyl)phenyl), which influence the optical and electronic properties of the resulting polythiophenes. Poly(3‐(2‐(4‐hexylbenzoyl)phenyl)thiophene) was found to have lower frontier orbital energy levels (HOMO/LUMO=−5.9/−4.0 eV) than poly(3‐hexylthiophene) owing to the electron‐withdrawing ability of the aryl ketone side chains. The electron mobility (ca. 2×10−3 cm2 V−1 s−1) for poly(3‐(2‐(4‐hexylbenzoyl)phenyl)thiophene) was found to be significantly higher than the hole mobility (ca. 8×10−6 cm2 V−1 s−1), which suggests such polymers are candidates for n‐type organic semiconductors. Density functional theory calculations suggest that backbone distortion resulting from side‐chain steric interactions could be a key factor influencing charge mobilities.