Enol and Ynol Surrogates: Promising Substrates for Hypervalent Iodine Chemistry

Abstract

This reviewisd edicated to Prof. Jean Lessard on the occasion of his 80th birthday Asian Abstract: In numerous iodine(III)-mediated methodologies that involve ketone compounds, the enol tautomer is expected to be the reactive species. In this context,t he exploration of enol and ynol surrogates as substrates is of great interest. Activated p-systems have been shown to exhibit interesting and highly exploitable behavior towardh ypervalent iodine reagents. This has led to the development of nu-merousu seful oxidativet ransformations. Enamines, enamides, enol derivatives, haloalkenes, and haloalkynes are all enol or ynol surrogates that are reactivet owards the most populari odanes and iodonium salts. This Focus Review will describep ast and on-going research involving these substrates to gain insighti nto the similarities and disparities observed in their reactivity profiles.The ORCID identification number(s) for the author(s) of this articlecan be found under http://dx.Scheme4.Proposed mechanism to explain 2 H-arizine formation and acetoxylation.Scheme5.Synthesis of 2-trifluoromethyloxazoles developed by Du, Zhao, and co-workers.Scheme6.Dichlorination of enaminesd evelopedbyZ hao, Du, and co-workers.Scheme7.Optimizedreductive conditionst oconvertthe dihaloimines to their corresponding enamines.

An α‐Cyclopropanation of Carbonyl Derivatives by Oxidative Umpolung

“…Ketones and their derivatives for instance are commonly employed in oxidative umpolung reactions. Classically promoted by toxic elements such as Hg(II), Tl(III), Pb(IV), or Se(IV) more modern variants rely on Bi(V), N ‐oxides, Mn(III), halosuccinimides, sulfoxides, and on iodine(III) …”

“…Classically promoted by toxic elements such as Hg(II), [9,10] Tl(III), [9,11] Pb(IV), [9,12,13] or Se(IV) [14] more modern variants rely on Bi(V), [15] N-oxides, [16][17][18][19] Mn(III), [20,21] halosuccinimides, [22] sulfoxides, [23] and on iodine(III). [24][25][26][27][28][29] The a-functionalization of certain ketones through oxidative umpolung with iodine(III) was pioneered already in the 1960s, [30,31] has been extensively investigated in the 1980s, [32][33][34][35][36] and gained further attention in more recent years. [37][38][39][40][41] It is believed that the reaction involves an enolonium species (compound 8, Scheme 1 a).…”

The ortho‐Difluoroalkylation of Aryliodanes with Enol Silyl Ethers: Rearrangement Enabled by a Fluorine Effect

“…This type of reaction has experienced significant advances in the past three decades. Although the mechanism still remains elusive, the umpolung of ESEs by aryliodanes is generally accepted as a key step in these transformations (Scheme a) –. Under the oxidation effect of hypervalent iodine reagents, the conventionally nucleophilic ESEs can react either with themselves or other nucleophilic coupling partners to form the self‐coupling products, or other α‐functionalized carbonyls–, respectively, with phenyl iodides as byproducts.…”

Iodine(III)-Mediated Oxidative Hydrolysis of Haloalkenes: Investigation of the Effect of Iodine(III) Reagents

“…In this regard, we have initially developed new chiral precatalysts for the enantioselective iodine(III)-promoted α-tosyloxylation of ketones (Scheme 1A). 8 Selectivity issues encountered in our group and others 9 for this transformation led us to investigate enol surrogates, 10 in particular enol esters, 11 to access these products (Scheme 1B). From the success of this recent work, we then explored the use of haloalkenes as possible substrates to access similar α-substituted ketones (Scheme 1C).…”