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. 2020 Jul 1:16:1579-1587.
doi: 10.3762/bjoc.16.130. eCollection 2020.

Azidophosphonium salt-directed chemoselective synthesis of (E)/(Z)-cinnamyl-1 H-triazoles and regiospecific access to bromomethylcoumarins from Morita-Baylis-Hillman adducts

Soundararajan Karthikeyan  1 , Radha Krishnan Shobana  1 , Kamarajapurathu Raju Subimol  2 , J Helen Ratna Monica  1 , Ayyanoth Karthik Krishna Kumar  1
Affiliations

Azidophosphonium salt-directed chemoselective synthesis of (E)/(Z)-cinnamyl-1 H-triazoles and regiospecific access to bromomethylcoumarins from Morita-Baylis-Hillman adducts

Soundararajan Karthikeyan et al. Beilstein J Org Chem. .

Abstract

The direct transformation of Morita-Baylis-Hillman (MBH) adducts into molecules of interest is a crucial process wherein allylic hydroxy-protected or halogenated MBH adducts are commonly preferred. Herein, we report an azidophosphonium salt (AzPS)-catalysed straight forward protocol for synthesising structurally demanding (E)/(Z)-cinnamyl-1H-1,2,3-triazoles and halomethylcoumarins from MBH adducts. The novel methodology, efficient catalyst, and direct utilization of MBH adducts under mild reaction conditions qualify the reported procedures as powerful synthetic tools.

Keywords: Morita–Baylis–Hillman adducts; halomethylcoumarin; organocatalyst; phosphonium salt; triazolation.

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Figures

Scheme 1
Scheme 1
Literature-reported cycloaddition reactions of MBH acetates involving azides and alkynes [–28].
Scheme 2
Scheme 2
Synthetic methodologies for triazolations of MBH adducts. a) Literature-reported indirect triazolation of MBH adducts [–33]. b) This work: phosphonium salt-catalysed triazolation of MBH adducts.
Scheme 3
Scheme 3
Scope of the one-pot cascade reaction of the unprotected Morita–Baylis–Hillman adducts 3a–q.
Figure 1
Figure 1
Proposed mechanism for the synthesis of 1,4-disubstituted triazoles.
Scheme 4
Scheme 4
Comparative analysis of the sequential one-pot reaction.
Figure 2
Figure 2
Proposed mechanism for the synthesis of 3-(bromomethyl)coumarins.
See this image and copyright information in PMC

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