Electrophilic iodine(i) compounds induced semipinacol rearrangement via C–X bond cleavage

Abstract

Neutral electrophilic iodine(I) species proved to be efficient reagents for C-X bond cleavage of various cyclic and acyclic α-silyloxyhalides, and the induced desilylative semipinacol rearrangement provided the corresponding ketones in good yields. The reaction is operationally simple, and proceeds under mild conditions with good functional group compatibility. Mechanistic investigations, including computational studies, were also performed.

Halogen Bonding in Organic Synthesis and Organocatalysis

“…Subsequently, Tsuji, Kobayashi, and Takemoto introduced N ‐iodo‐based halogen‐bond donors, such as N ‐iodosuccinimide (NIS), as powerful activators in a halogen‐bond‐induced semipinacol rearrangement reaction (Scheme ) . In the proposed reaction mechanism, NIS cleaves the carbon–bromine (or carbon–chlorine) bond of the substrate through a halogen‐bonding interaction, leading to the formation of a carbocation, which undergoes rearrangement.…”

New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation

“…Considering the electrophilic nature of a halogen in such molecules, these compounds could serve as effective halogen bond donors. In 2014, Takemoto and co-workers reported that electrophilic N -iodinated compounds could induce a semipinacol rearrangement (Scheme 22) [93]. Thus, the benzyl bromide moiety of substrates was activated upon treatment with N -iodosuccinimide (NIS) in nitromethane.…”

Synthesis and Evaluation of Azolium‐Based Halogen‐Bond Donors

“…Huber first demonstrated that halogen-containing organocatalysts were competent activators of carbon-heteroatom bonds towardsn ucleophilic displacement in 2011. [3] Following this disclosure, reports on av ariety of other reactions promotedb yi odine-containingh alogen bond catalysts including (aza)-Diels-Alder, [4] Michael addition, [5] halidea bstraction, [6] semipinacolr earrangement, [7] and cooperative catalysis by silica activation [8] have also appeared. These examples highlight the potential of halogen-bondingo rganocatalystst of acilitatek nown acid-promoted reactions, but at a more fundamentall evel, ac lear model for their modeo fa ction remains undefined.…”

“…With the optimizedc onditions for the iodination of 1,2,4-triazoles in hand, we synthesized electronically and sterically differentiated chiral and achiral triazolium and imidazolium salts ( Table 2). Several chiral triazolium salts that are prominent in NHC catalysis were iodinated in high yields, including the widely used aminoindanol scaffold (6), as well as sterically hindered chiral catalysts (7), which are known to possessv astly differente lectronic properties. [14] Additionally,w ef ound the methodt ob eg eneral to convert other N-heterocyclic scaffolds used in NHC catalysis to their iodinated derivatives, for example benzimidazolium (9)a nd imidazopyridinium (10)d erivatives were also synthesized in excellenty ields using our protocol (> 95 %).…”

“…We next revisited the conjugate addition reaction of indoles with enones to evaluatec hiral 1,2,4-triazolium based halogen bondings caffolds, since no one has reported enantioinduction using chiral halogen bondingc atalysis. While these chiralm otifs have been very successful for asymmetric NHC catalysis,compounds 6,7,8,16,17 and 18 all failed to promote the conjugate addition reaction( catalyst 18 produced an analytically observable amount of product which was verified as racemic).…”