Concise synthesis of α-substituted 2-benzofuranmethamines and other 2-subsituted benzofurans via α-substituted 2-benzofuranmethyl carbocation intermediates

Nikhom Wongsa, Ubonta Sommart, Thunwadee Ritthiwigrom, Arife Yazici, Somdej Kanokmedhakul, Kwanjai Kanokmedhakul, Anthony C. Willis, Stephen G. Pyne*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    29 Citations (Scopus)

    Abstract

    Propargyl amines 4, where R3 is aryl, undergo 5-exo-dig cyclization reactions under relatively mild conditions (AgNO3, DMF, 60 C, 1 h) to give 3-amino-2,3-dihydro-2-arylmethylidenebenzofurans 5 (R 3 = aryl). In contrast, substrates where R3 is alkyl undergo competing 6-endo-dig and 5-exo-dig cyclization processes. The hydroxymethyl substrate 4 (R3 = CH2OH), however, was smoothly converted to its corresponding 5-exo-dig cyclization product 5, likely due to the assistance of the primary hydroxyl group in the 5-exo-dig cyclization process by silver cation coordination. Under more enforcing conditions (AgNO3, DMF, 100 C, 18 h), the initially formed products 5 undergo a 1,3-allylic rearrangement to their corresponding 2-substituted benzofuran derivatives 6. This rearrangement can also be effected by treating 5 with AgNO3 in DMF at 100 C for 18 h or BF3·Et 2O at rt. 2-(3-Butenyl)benzofurans 7 (Nu = allyl) can be prepared by treatment of 5 with BF3·Et2O and allyltributylstannane. Furan and MeOH could also be employed as external nucleophiles in these BF3·Et2O-promoted reactions.

    Original languageEnglish
    Pages (from-to)1138-1148
    Number of pages11
    JournalJournal of Organic Chemistry
    Volume78
    Issue number3
    DOIs
    Publication statusPublished - 1 Feb 2013

    Fingerprint

    Dive into the research topics of 'Concise synthesis of α-substituted 2-benzofuranmethamines and other 2-subsituted benzofurans via α-substituted 2-benzofuranmethyl carbocation intermediates'. Together they form a unique fingerprint.

    Cite this