Aromatic [5,5]-sigmatropic rearrangement is an appealing protocol for accessing 1,4-substituted arenes.H owever,s uch ap rotocol has not been well utilized in organic synthesis because of the difficulties in the synthesis of the substrates,s electivity issues,a nd limited substrate scope. Described herein is an ew [5,5]-sigmatropic reaction utilizing readily available aryl sulfoxides and allyl nitriles.This reaction features mild reaction conditions,high chemo-and regioselectivity,e xcellent functional-group compatibility,a nd broad substrate scope.Computational studies suggest that the success of the reaction can be attributed to the selective electrophilic assembly of the rearrangement precursors,i nw hich al inear -C = C = N-linkage favors [5,5]-sigmatropic rearrangement over the competitive [3,3]-sigmatropic rearrangement. Scheme 1. Backgrounda nd this work.
The redox-neutral ortho-functionalizations of aryl/heteroaryl sulfoxides via interrupted Pummerer processes have been greatly advanced since its discovery by Kita and Padwa in the early 2000s. In this context, we recently developed an ortho-cyanoalkylation of aryl sulfoxides with alkyl nitriles using an ‘assembly/deprotonation’ protocol. The success of the reaction hinges on the independent control of the electrophilic assembly of both coupling partners and subsequent deprotonation of the in situ generated imine sulfonium intermediates. Further [3,3]-sigmatropic rearrangement of the in situ formed ketenimine sulfonium species furnishes ortho-cyanoalkylated aryl sulfides. More recently, we also applied the ‘assembly/deprotonation’ strategy for the development of the [5,5]-sigmatropic rearrangement of aryl sulfoxides with allyl nitriles that allows for para-cyanoalkylation of aryl sulfoxides. The development of these two reactions is described in this Synpacts article.1 Background2 [3,3]-Sigmatropic Rearrangement3 [5,5]-Sigmatropic Rearrangement4 Conclusion
Aromatic [5,5]-rearrangement can in principle be an ideal protocol to access dearomative compounds. However, the lack of competent [5,5]-rearrangement impedes the advance of the protocol. In this Article, we showcase the power of [5,5]-rearrangement recently developed in our laboratory for constructing an intriguing dearomative sulfonium specie which features versatile and unique reactivities to perform nucleophilic 1,2- and 1,4-addition and cyclization, thus achieving dearomative di- and trifunctionalization of easily accessible aryl sulfoxides. Impressively, the dearomatization products can be readily converted to sulfur-removed cyclohexenones, naphthalenones, bicyclic cyclohexadienones, and multi-substituted benzenes. Mechanistic studies shed light on the key intermediates and the remarkable chemo-, regio- and stereoselectivities of the reactions.
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