Synthesis of Phenanthridine Derivatives by Microwave-Mediated Cyclization of o-Furyl(allylamino)arenes

Abstract

A novel and efficient synthesis of phenanthridines and aza analogues is reported. The key step is a microwave-mediated intramolecular Diels-Alder cyclization of o-furyl(allylamino)arenes. In the presence of a catalytic amount of acid, the DA-adduct reacts further to give the dihydrophenanthridines, which easily can be oxidized to fully aromatic compounds by air in the presence of UV light or by DDQ.

Mechanistic Investigation of the Reaction of Epoxides with Heterocumulenes Catalysed by a Bimetallic Aluminium Salen Complex

“…No formation of alcohol 4b or ketone 5b was observed. It is worth noting that this N ‐crotylaniline cyclized considerably more slowly than the corresponding N ‐allylaniline studied under the same conditions previously,6 but N ‐allylfurylamines might be quite sensitive to steric effects in the dienophile part of the molecule 4b . N ‐Allylamines are normally believed to be stable under acidic conditions and show good tolerance of, for instance, acid‐mediated reduction of nitro groups,15 hydrolysis of amides,16 and deformylations,17 but loss of allylic moieties from N ‐allylnaphthylamines was reported as a side reaction when aza‐Claisen rearrangements at elevated temperatures were attempted 18.…”

“…We have previously shown that the presence of electron‐withdrawing substituents ortho and para to the allylamino group increases the reactivity in IMDAF cycloaddition 5. The anilines 1 5,6 were N ‐alkylated with crotyl bromide to give the IMDAF substrates 2 (Scheme ).…”

“…The presented calculated NMR shifts and coupling constants of the cis and trans isomers of compound 4b are the Boltzmann‐weighted sum of their two conformers. Compounds available by literature methods: 1a ,5 1b 6…”

“…We have previously shown that allylamino‐ or allyloxyfuryl(hetero)arenes can undergo IMDAF cycloaddition to give complex fused polycyclic heterocycles 5. Furthermore, we have developed a new and efficient synthesis of phenanthridines (Figure 1), as well as their aza analogues, functionalized in the A‐ring by use of microwave‐mediated intramolecular Diels–Alder cyclization of ortho ‐furyl(allylamino)arenes as a key step 6. Here we report the outcomes of these processes when substituted allyl groups are used as dienophiles in IMDAF cycloaddition under microwave conditions or on conventional heating.…”

Furan Çekirdekli Bileşiklerin Mikrodalga Destekli Molekül İçi Diels Alder Halkalaşma Reaksiyonları

“…Yan zincir kısmında (tether de) N-KG ve O içeren furan çekirdekli bileşiklerin organik kimyada oldukça zor olan trisiklik ve tetrasiklik fused halkalaşma ürünleri tek adımda Termal ve mikrodalga yöntemle intramoleküler [4+2] Diels-Alder reaksiyonları sonucu elde edilebilmektedir [3,4].…”