Abstract
Synthesis of novel pyrazole-fused heterocycles, i.e., dihydro-1H- or 2H-oxepino[3,2-c]pyrazoles (6 or 7) from 4-allyloxy-1H-pyrazoles (1) via combination of Claisen rearrangement and ring-closing metathesis (RCM) has been achieved. A suitable catalyst for the RCM of 5-allyl-4-allyloxy-1H-pyrazoles (4) was proved to be the Grubbs second generation catalyst (Grubbs2nd) to give the predicted RCM product at room temperature in three hours. The same reactions of the regioisomer, 3-allyl-4-allyloxy-1H-pyrazoles (5), also proceeded to give the corresponding RCM products. On the other hand, microwave aided RCM at 140 °C on both of 4 and 5 afforded mixtures of isomeric products with double bond rearrangement from normal RCM products in spite of remarkable reduction of the reaction time to 10 min.
Highlights
Because pyrazoles are important heterocyclic compounds with diverse bioactivities, extensive studies have been carried out for the synthesis of substituted or functionalized pyrazoles [1,2,3,4,5].most of them are based on the construction of a pyrazole ring by the [2 + 3] cycloaddition of already substituted parts [6,7,8]
Pyrazole-fused heterocycles have been recently synthesized because they exhibit diverse important biological activities; they could not be synthesized from substituted monocyclic pyrazole derivatives [15]
Dihydrooxepino[3,2-c]pyrazoles, from 1 via the combination of Claisen rearrangement and ring-closing metathesis (RCM) and divergence of RCM products depending on reaction conditions
Summary
Because pyrazoles are important heterocyclic compounds with diverse bioactivities, extensive studies have been carried out for the synthesis of substituted or functionalized pyrazoles [1,2,3,4,5].most of them are based on the construction of a pyrazole ring by the [2 + 3] cycloaddition of already substituted parts [6,7,8]. Because pyrazoles are important heterocyclic compounds with diverse bioactivities, extensive studies have been carried out for the synthesis of substituted or functionalized pyrazoles [1,2,3,4,5]. Direct functionalization of pyrazoles has been rarely reported; it is a synthetic challenge. Pyrazole-fused heterocycles have been recently synthesized because they exhibit diverse important biological activities; they could not be synthesized from substituted monocyclic pyrazole derivatives [15]. Sildenafil citrate, a well-known clinically approved erectile dysfunction improving drug Viagra® , is one of the representative example possessing a pyrazole-fused bicyclic structure (Figure 1) [15,16]. Synthesis of novel pyrazole-fused heterocycles is extremely important for drug discovery and is a great challenge in organic chemistry
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
