Morita–Baylis–Hillman‐Type [3,3]‐Rearrangement: Switching fromZ‐ toE‐Selective α‐Arylation by New Rearrangement Partners

Abstract

a-aryl a,b-unsaturated carbonyls represent an important class of derivatizable synthetic intermediates,h owever,the synthesis of such compounds still remains achallenge. Recently,weshowcased anovel Z-selective a-arylation of a,bunsaturated nitriles with aryl sulfoxides via [3,3]-rearrangement involving an Morita-Baylis-Hillman (MBH) process. Herein, we demonstrate the feasibility of reversing the stereoselectivity of such MBH-type [3,3]-rearrangement by switching to an ew pair of rearrangement partners consisting of aryl iodanes and a,b-unsaturated oxazolines.A saresult, the two protocols complement each other in approaching E-or Z-aaryl a,b-unsaturated carbonyl derivatives.M echanistic studies reveal apossible reaction pathway and provide an explanation for the opposite stereoselectivities.

Updates on hypervalent-iodine reagents: metal-free functionalisation of alkenes, alkynes and heterocycles

“…The products formed show remarkable E -selectivity which might be due to final trans -β-H-elimination (Scheme 14). 63…”

“…The products formed show remarkable E-selectivity which might be due to final trans-β-H-elimination (Scheme 14). 63 Ali and co-workers demonstrated HVI(III) mediated regioand diastereoselective aminobromination of electron-deficient olefins ( 23) using the group-assisted purification (GAP) method. The authors reported a unique strategy of synthesising vicinal bromoamines (24) by simply mixing GAP auxiliaryanchored substrates with TsNH 2 -NBS as nitrogen/bromine sources and PhI(OAc) 2 as a catalyst.…”

Lewis Base‐assisted Arylation of Unsaturated Carbonyls

“…This selectivity stands out even more when compared to a similar process developed shortly after and utilizing I(III) (18) instead of S(IV) in combination with vinylic oxazoles 19 (Scheme 5B). [13] Therein, electrophilic activation is achieved using TMSOTf and a rearrangement (20) conceptually similar to that shown in Scheme 5A leads to o-iodo vinyl arenes 21, exclusively with E-configuration again attributed to a selective E1cB elimination step, as supported by quantum chemical computations.…”

“…Using the redox-active main group elements sulfur and iodine, Peng et al reported the arylation of specific electron-deficient alkenes via [3,3]-sigmatropic rearrangements. [12,13] Leveraging electrophilic activation of aryl sulfoxides (14) with triflic anhydride, addition of α,β-unsaturated nitriles ( 15) is enabled, leading to the assembly of complexes prone to attack by a subsequentially added nitrogen Lewis base (DABCO or 2-chloropyridine), forming ketenimine 16 in situ (Scheme 5A). Upon formation of 16, a [3,3]-sigmatropic rearrangement forms the desired new CÀ C bond and rearomatization follows.…”

Revisiting Aromatic Claisen Rearrangement Using Unstable Aryl Sulfonium/Iodonium Species: The Strategy of Breaking Up the Whole into Parts

“… Further studies of the discovery led us to recognize two critical strategies that did not exist in traditional Claisen rearrangement but could serve as a guide for the development of this nontraditional rearrangement. One strategy is the division of the conventional one-step construction of rearrangement precursors into two or more steps that allows us to control each step of the reaction more precisely, thus not only expanding the substrate scope but also inspiring the development of [5,5]-sulfonium rearrangement, asymmetric iodonium rearrangement, and Morita–Baylis–Hillman (MBH)-type sulfonium/iodonium rearrangements. , The other strategy is the use of the effect of congestion-accelerated rearrangement for developing the rapid ketenimine-iodonium Claisen rearrangement, which further led to the first examples of the dearomatization of aryl iodanes . In this Account, we will provide an overview of these rearrangement reactions developed in our laboratory and will try to illustrate our logic behind these designs.…”