Studies on the syntheses of heterocyclic compounds-CDXXXVI

Construction of the 5,10b‐Phenanthridine Skeleton Using [3+2]‐Cycloaddition of a Non‐Stabilized Azomethine Ylide: Total Synthesis of (±)‐Maritidine and (±)‐Crinine Alkaloids

“…In this context, intramolecular oxidative para-para phenolic coupling [24][25][26][27][28] and Pictet-Spengler cyclization [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] of 3-aryl hydroindole derivatives have emerged as the two main strategies. In the former approach, spiro-fused dienone precursor 7 is obtained by the para-para coupling of substituted norbelladine derivatives employing various oxidizing agents, [24,25,27] photochemical cyclization, [26] intramolecular Heck reaction, [39] and cyclization of an intermediate iron carbonyl complex. [27,28] Substituted 3a-arylhydroindoles 6, which are used for the Pictet-Spengler reaction, are synthesized through key reactions such as regioselective reduction of 1-methyl-3,3-disubstituted pyrrolidine-2,5-dione, [30] intramolecular ene cyclization [31] of an appropriately constructed acylnitroso olefin, or condensation of 3-arylated Δ 1 -pyrrolinium salts with tert-butyl 3-oxopent-4-enoate.…”

Electrophilic C12 Building Blocks for Alkaloids: 1,1 Iterative Organoiron‐Mediated Routes to (±)‐Lycoramine and (±)‐Maritidine

“…[44] In 1996, Kita et al [45] made an important contribution to the syntheses of maritidine and later galanthamine-type alkaloids, [46] when they reported the use of PIFA as a suitable oxidising agent for intramolecular oxidative phenolic couplings reactions. This route was modified by Ley et al [47] to synthesise (Ϯ)-oxomaritidine and (Ϯ)-epimaritidine using only polymersupported reagents.…”

Benzylic hydroxylations of the Amaryllidaceae alkaloids

“…These discoveries plus the reports of the successful incorporation of protocatechuic aldehyde (8,9,10) The possibility of other Cs-Ci precursors was reported by Barton and coworkers (l8), who found that N-Emethyl-^^C]-3-hydroxy-4-[inethoxy-^ "^Cjbenzylamlne (12) was incorporated into galanthamine (13) and haemanthamine (2). Chemical degradations established that all of the radioactivity was located in the methoxyl group of.galanthamine (33) and the methylenedioxy group of haemanthamine (2). They rationalized NHCH CH,0 12 13 their results by suggesting that (1^) was degraded to isovanlllin or to 3-hydroxy-4-methoxybenzylamine and then incorporated into the alkaloids.…”

“…These approaches have in common the generation of a phenyl radical or a phenoxonium ion in a norbelladine-type system. Barton Kametani and coworkers (32,33,34) have also carried out the cycllzatlon of norbelladine-type systems by generating a radical species via photolytic heterolysis of a carbonbromine bond. When 2-bromo-N-(4-hydroxyphenethyl)-4,5methylenedioxybenzylamine (2^) was photolyzed, (±)-oxocrinine (2^) was obtained in 5% yield (32).…”

“…When 2-bromo-N-(4-hydroxyphenethyl)-4,5methylenedioxybenzylamine (2^) was photolyzed, (±)-oxocrinine (2^) was obtained in 5% yield (32). An analogous route was employed tr obtain (±)-oxomaritidine (33). When N-(^-hydroxyphenethyl)-N-3,4-methylenedioxybenzyl trifluoroacetamide (^) was oxidized with thallium(III) tri-fluoroacetate5 followed by hydrolysis of the amide, (±)-oxocrinine (2_4) was obtained in 13% yield (35).…”