Synthesis of 2-substituted chromenes via ring-closing metathesis and stable 1-benzopyrylium ions

Mapping the Catechol Binding Site in Dopamine D1Receptors: Synthesis and Evaluation of Two Parallel Series of Bicyclic Dopamine Analogues

“…Deoxygenation of such lactol systems with boron trifluoride diethyl etherate (BF 3 ·OEt 2 ) results in formation of oxonium ions, which in turn may be reduced with a hydride source [22] or trapped with an appropriate nucleophile. [23, 24] A deep red color was formed, indicative of the oxonium ion, but attempts to trap it with a variety of electrophilic reagents such as cyclohexylMgCl, phenylMgBr, adamantylMgCl, or adamantylZnCl at either 0 °C or −78 °C yielded numerous products. Triethylsilane did prove to be an effective hydride source to yield the unsubstituted 10 (Scheme 2).…”

Metal-Catalyzed Intermolecular Hydrofunctionalization of Allenes: Easy Access to Allylic Structures via the Selective Formation of C–N, C–C, and C–O Bonds

“…243 In 2000 Rutjes described the palladium-catalyzed hydroalkoxylation of allenes with phenols bearing a free-alkene in ortho, as a key step for the synthesis of chromenes via ring-closing metathesis (Scheme 123). 263 Noteworthy, the reaction proceeded at room temperature and allowed the formation of the diene in only one minute. Similar conditions were also used for the obtention of allylic O,O-and N,O-acetals with aliphatic and aromatic alcohols.…”

Palladium-catalysed inter- and intramolecular formation of C–O bonds from allenes

“…Whole etherification of 1,3,5-trihydroxybenzene has also been carried out (eqn ( 9)). 16 With the Rutjes procedure, the hydroaryloxylation of benzyloxyallene effectively happens in a few seconds at room temperature (eqn (10)), 11,17 while that of methoxyallene requires reflux and results in low yields. 17 The reason for this remarkable difference was unexplained.…”

“…Annelation of allenes with vinylic halides bearing an alcohol group led Larock's team to isolate a variety of heterocycles (eqn (17) to ( 19)) through, probably, Z 3 -allylpalladium intermediates, the reaction being enantioselective in using chiral ligands (eqn (17)). 19,20,24 With 2-iodo-3-methylbut-2-en-1-ol, the Z 1 -or Z 3 -allylpalladium intermediate inserts a second allene before closing to a seven-membered heterocycle (eqn ( 19)).…”