Metal-Free Transfer Hydroiodination of C–C Multiple Bonds

Abstract

The design and a gram-scale synthesis of a bench-stable cyclohexa-1,4-diene-based surrogate of gaseous hydrogen iodide are described. By initiation with a moderately strong Brønsted acid, hydrogen iodide is transferred from the surrogate onto C−C multiple bonds such as alkynes and allenes without the involvement of free hydrogen iodide. The surrogate fragments into toluene and ethylene, easy-to-remove volatile waste. This hydroiodination reaction avoids precarious handling of hydrogen iodide or hydroiodic acid. By this, a broad range of previously unknown or difficult-to-prepare vinyl iodides can be accessed in stereocontrolled fashion.

Regioselective Hydroiodination of Alkynes by in situ‐Generated HI

“…Their approach is based on the trapping of a transfer hydrogenation intermediate like vinyl copper complex . Oestreich and co‐workers introduced an improved metal‐free transfer hydroiodination of alkynes for the preparation of vinyl iodide using HI surrogate . Hydroiodination of alkynes by the in situ generated HI using different reagents have also been successfully developed (Scheme ) –.…”

Iridium‐Catalyzed Hydrochlorination and Hydrobromination of Alkynes by Shuttle Catalysis

“…Research Articles alkynes.Abroad range of functional groups,including nitriles (8), chlorides (9), esters (10), amines (12), nitro (16), aryl chloride (17), aryl fluorides (18), iodide (19), aldehyde (22), and ketone (29)w ere tolerated. Likewise, a,b-unsaturated esters,which serve as an important building block in organic synthesis,w ere tolerated under the reaction conditions (15).…”

“…Recently,a na lternative method using at ransfer hydrofunctionalization strategy was reported by the groups of Lautens [18] and Oestreich. [19] They achieved the hydrobromination of 1,6-enynes and alkynes through the transfer of HBr from Et 3 N·HBr and 1-(2-bromoethyl)-1,4-dihydro-1,1'-biphenyl, respectively.I nt his context, we were delighted to see that our protocol for the transfer hydrochlorination using tert-butyl chloride could also be applied to the transfer hydrobromination using tert-butyl bromide as the source of HBr. We then decided to evaluate the scope and the potential of this transformation.…”

Ionic Transfer Reactions with Cyclohexadiene-Based Surrogates

“…By adding an additional substituent adjacent to the tether, we prevented this aromatization and had finally arrived at our HI surrogate 54. 64 Figure 3 Design of stable cyclohexa-1,4-diene-based surrogates of HI…”

“…However, under Brønsted acid catalysis and with a range of alkynes we could achieve hydroiodination to access valuable vinyl iodide products (Scheme 22). 64 An impressive functional group tolerance was demonstrated, with terminal phenylacetylenes containing halogens, aldehydes, nitriles, and boronate esters (56a-g) all amenable to the reaction. Internal alkynes were also compatible, and one substrate containing two alkynes could also be selectively reacted only once to give 56h.…”