An Unusual Example of a 6-Endo-Dig Addition to an Unactivated Carbon-Carbon Triple Bond
摘要:
Methyl 2-[2-[2-(1-hydroxy-1-ethyl)phenyl]ethynyl]benzoate was prepared as an intermediate for subsequent conversion to an a-diazo ketone. Under the basic conditions used to hydrolyze the methyl ester, the neighboring hydroxyl functionality underwent reaction with the unactivated acetylenic group, producing a benzopyranyl-substituted alpha-diazoacetophenone. Treatment of this diazocarbonyl compound with a catalytic quantity of rhodium(II) mandelate afforded a novel dibenzo[a,e]cyclononenone derivative. The reaction proceeds via an initially formed oxonium ylide which rearranges further by means of a 1,2-alkyl shift. A prime factor in determining the direction of internal cyclization to the triple bond is the presence of the carbomethoxy group in the ortho position of the beta-phenyl ring. Thus, in contrast with related systems which exhibit a clear preference for 5-exo-dig cyclization at the acetylenic center, the 6-endo-dig addition is the preferred pathway for the o-formyl- and o-carbomethoxy-substituted alkynyl alcohols. Careful monitoring of the reaction actually showed that the reaction proceeds by initial formation of the 5-exo-dig product followed by a novel rearrangement to the 6-endo product.
Rapid Access to Oxabicyclo[2.2.2]octane Skeleton through Cu(I)‐Catalyzed Generation and Trapping of Vinyl‐
<i>o</i>
‐quinodimethanes (
<scp>
Vinyl‐
<i>o</i>
‐QDMs
</scp>
)
<sup>†</sup>
作者:Hejiang Luo、Chuan He、Huanfeng Jiang、Shifa Zhu
DOI:10.1002/cjoc.202000144
日期:2020.10
A Cu(I)‐catalyzed three‐component reaction of terminal enynals/enynones, diazo compounds, and alkenes has been developed. With this method, a series of oxabicyclo[2.2.2]octanes were effectively synthesized in high yields under mild reaction conditions. This transformation is proposed to proceed through trapping of the cyclic vinyl‐o‐quinodimethanes (vinyl‐o‐QDMs) species, which were generated from
An Efficient Gold-Catalyzed Domino Process for the Construction of Tetracyclic Ketoethers
作者:Tobias Groß、Peter Metz
DOI:10.1002/chem.201302985
日期:2013.10.25
Au, yeah! Catalytic amounts of gold(III)chloride allow a mild and efficient oxidative domino cyclization/cycloaddition of enyne carbonyl compounds 1 and 4 to give the tetracycles 2 or 5, respectively, in the presence of pyridine N‐oxide 3 (see scheme; DCE = 1,2‐dichloroethane).
Discovery of a Photoinduced Dark Catalytic Cycle Using <i>in Situ</i> LED-NMR Spectroscopy
作者:Dan Lehnherr、Yining Ji、Andrew J. Neel、Ryan D. Cohen、Andrew P. J. Brunskill、Junyu Yang、Mikhail Reibarkh
DOI:10.1021/jacs.8b08596
日期:2018.10.24
We report the use of LED-NMR spectroscopy to study the reaction mechanism of a newly discovered photoinduced iron-catalyzed cycloisomerization of alkynols to cyclic enol ethers. By understanding on/off ligand binding to the catalyst, we were able to appropriately design reaction conditions to balance catalyst activity and stability. LED-NMR was demonstrated to be a powerful tool in elucidating reaction mechanisms of photochemical reactions. Temporal NMR spectroscopic data under visible light illumination (1) revealed the pre-catalyst activation mechanism, (2) proved that photon flux provides a unique external control of the equilibrium distribution between the pre-catalyst and active catalyst, and ultimately the rate of reaction, (3) provided information about the reaction driving forces and the turnover-limiting step, and (4) enabled both real-time structural and kinetic insights into elusive species (e.g., dissolved gases).