Protic‐Solvent‐Mediated Cycloisomerization of Quinoline and Isoquinoline Propargylic Alcohols: Syntheses of (±)‐3‐Demethoxyerythratidinone and (±)‐Cocculidine

Abstract

Eine Cycloisomerisierungsstrategie zur Synthese von Benz[g]indolizinonen und Benz[e]indolizinonen bietet die erste allgemeine Route zu diesen einzigartigen Azacyclen (siehe Beispiel). Die Benzindolizinon‐Produkte wurden in der Totalsynthese der Erythrina‐Alkaloide 3‐Demethoxyerythratidinon und Cocculidin eingesetzt.

Total Syntheses of (−)‐Huperzine Q and (+)‐Lycopladines B and C

“…[14] In all cases, a regiospecific metathesis reaction was observed, and only the desired product 13 was detected, presumably owing to the high torsional strain that exists in the disfavored bridged product 12. Remarkably, to the best of our knowledge, only a few examples have been reported for the use of Schrock molybdenum alkylidene complex 11 for a carbonyl-olefin metathesis in natural product synthesis, [12] and our reaction is a rare example of ethylene-accelerated carbonyl-olefin metathesis.…”

“…With 7 in hand, a direct metathesis between the alkene and carbonyl moieties (carbonyl-olefin metathesis) was explored to furnish the desired cyclopentene ring. [11,12] After extensive reaction optimization, we were pleased to find that in the presence of ethylene gas (1 atm), 13 could be obtained in moderate yield (48 % yield of isolated product, 75 % based on recovered starting material). Control experiments showed that ethylene probably played two crucial roles during the process: 1) It increased the catalyst reactivity by means of converting the bulky complex 11 into the more active species {Mo = CH 2 }, [13] and 2) it reacted with the remaining molybdenum alkylidene intermediate 14 to avoid the formation of side products and to recover substrate 7.…”

Halogen Bond Catalysis on Carbonyl–OlefinRing‐ClosingMetathesis Reaction: Comparison with Lewis Acid Catalysis

“…[ 2 ] The carbonyl–olefin metathesis reaction may directly form carbon‐carbon bonds between carbonyl and olefin functional groups and synthesizes desired products. [ 3 ]…”

Oxygen as a Heteroatom in Propargylic Alcohols: Reactivity, Selectivity, and Applications

“…The applications of propargylic alcohols [1] in many useful transformations, significant utilization in total synthesis, [2][3][4][5][6][7]9] and in construction of many heterocyclic compounds [8][9] and their derivatives have gained much attention and have been extensively investigated. Recent developments on the chemistry of propargylic alcohols and their derivatives disclosed a variety of highly efficient Lewis acid-catalyzed cascade reactions based on Meyer-Schuster rearrangement [10][11][12] (MSR) of propargylic alcohols, [3,3] rearrangement of propargylic acetates and intramolecular cyclization of propargylic alcohols, tethered with nucleophiles.…”