Flexible metathesis-based approaches to highly functionalised furans and pyrroles

Transition Metal-Mediated Synthesis of Monocyclic Aromatic Heterocycles

“…222 The aromatization step was achieved by the acid-mediated methanol elimination. This methodology was successfully applied for the preparation of pyrrolofuran 2-450 and bifuran 2-451 , as well as for a facile assembly of the disubstituted furan moiety ( 2-452 ) in the total synthesis of (−)- Z -deoxypukalide (Scheme 126).…”

“…222b,224 The reaction produces furans in moderate yields and is more efficient for the synthesis of disubstituted products. Cyclization of substrates possessing 1,1-disubstituted double bond of the homoallyl moiety, as well as bulky R 2 -substituents at the vinyl ether double bond was not efficient.…”

Ring‐Closing Metathesis: Novel Routes to Aromatic Heterocycles

“…A successful protocol was developed to access a range of substituted furans by synthesising the corresponding unsymmetrical acetals 32 (Scheme 9). [37,38] These acetals were readily produced from the allylic alcohols 31 by coupling with methoxyallene under palladium catalysis conditions. [39][40][41] The RCM reactions proceeded in excellent yields using catalyst 2 and the dihydrofuran 33 collapsed to reveal the aromatic compound upon treatment with TFA.…”

Palladium-catalyzed approach to the synthesis of five-membered O-heterocycles

“…By utilizing a palladium-catalyzed coupling reaction with methoxyallene, allylic alcohols can be converted into substrates that are ideal precursors to ring closing metathesis. After the RCM reaction is complete, the addition of acid promotes an elimination of methanol to form the fully aromatized system (Scheme 20) [65].…”