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Conjugation and Reactions of Conjugated Compounds
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Yes! This particular [3,3]-sigmatropic rearrangement is called the Claisen rearrangement. What is the product when allyl phenyl ether is heated?
Copper-assisted synthesis of five-membered O-heterocycles
Published in Inorganic and Nano-Metal Chemistry, 2020
Navjeet Kaur, Yamini Verma, Neha Ahlawat, Pooja Grewal, Pranshu Bhardwaj, Nirmala Kumari Jangid
The oxonium ylide underwent [1,2]-shift (Stevens rearrangement) as a major reaction. The [1,2]-shift has higher activation barrier as compared to orbital symmetry-allowed concerted [2,3]-sigmatropic rearrangement. [1,2]-Shift occurred in stepwise manner through the formation of radical pair intermediates.[134,135] Bridged or medium-sized cyclic compounds were synthesized when cyclic oxonium ylide was formed followed by [1,2]-shift.[136–139] West et al.[140] constructed cyclooctanoid ring system based on this strategy. Diazo ketones were treated with Cu(hfacac)2 (10 mol%) at reflux in dichloromethane to deliver a five-membered oxonium ylide which underwent a [1, 2]-shift to afford a structure which was transformed to final product, which was utilized for the preparation of natural products with fused five to six bicyclic frameworks. Other reaction pathways were possible from metal carbene intermediate. The reaction afforded intramolecular carbon–hydrogen insertion products primarily when Rh(II) triphenylacetate [Rh2(O2CCPh3)4] or rhodium acetate is employed as a catalyst. The diazo ketones were treated with Cu(tfacac)2 at reflux in dichloromethane, conditions for ylide formation/[2, 3]-sigmatropic rearrangement, to afford various unidentified products in low yields (Scheme 48).[1b]
Understanding the molecular mechanism of thio-Claisen rearrangement of allyl phenyl sulfide and allyl vinyl sulfide using bonding evolution theory coupled with NCI analysis
Published in Journal of Sulfur Chemistry, 2018
Arezu Nouri, Ehsan Zahedi, Morteza Ehsani, Azita Nouri, Ebrahim Balali
[3,3]-Sigmatropic rearrangement is an important class of pericyclic reactions in which a sigma bond migrates over a conjugated system to a new site [1]. The oldest known example of [3,3]-sigmatropic rearrangement was first described by Claisen in 1912 [2]. The thermal [3,3]-sigmatropic rearrangement of allyl phenyl sulfides or allyl vinyl sulfides (see Scheme 1) are sulfur analog of the simple Claisen rearrangement and known as the thio-Claisen rearrangement (TCR) [3]. The TCR is associated with the breaking of carbon–sulfur bond and formation of new carbon–carbon bond to yield a γ,δ-unsaturated thiocarbonyl compound [4].