A Stereoselective Palladium‐Mediated Reductive Coupling of Electron‐Deficient Terminal Iodoalkenes

Abstract

Iodoacrylate esters undergo palladiumcatalysed reductive homocoupling to derive dienyl diester derivatives. This reductive coupling can be extended to ester-substituted terminal iododienes to derive tetraene diesters. In all cases, the reactions show relatively high levels of stereocontrol, which shows an inversion of stereochemistry about one iodoalkene unit. This process, and the suggestion that the reaction releases diiodine, is consistent with a syn-1,2-addition of an iodopalladium(II)-alkene species across another iodoalkene unit (carbometallation step), followed by reductive syn-elimination of iodopalladium iodide to derive palladium(II) iodide. It appears that under the reaction conditions employed, palladium(II) iodide may equilibrate to palladium(0) and diiodine, which can be observed or trapped out from the reaction mixture.

Synthetic utility of tribenzyltin hydride and its derivatives as easily accessible, removable, and decomposable organotin reagents

“…The isolated products 8 were identified by 1 H and 13 C NMR analysis. The NMR data well agree with the reported data (8a [31], 8b [32], 8c [33] …”

Studies towards the synthesis of the northern polyene of viridenomycin and synthesis of Z-double bond analogues

“…As previously reported, 3c the benefit of using tri(o-tolyl)phosphine was primarily to provide steric bulk around the palladium(II) intermediate species, in order to prevent competitive iodide homocoupling. 5 We have already mentioned that this substrate does not undergo reductive dimerisation, which seems more likely to do with the difficultly in adding palladium across an aromatic double bond rather than any steric differences, and hence, because…”

“…It should be noted that the HM reactions of iodide 5 are non-trivial due to competition from the competing reductive dimerisation side-reaction. 5 Indeed, we have previously reported that employing tri(o-tolyl)phosphine is one of the few ways of suppressing this reaction. 3c The results of these studies were not initially promising (see Table 1), since the use of the standard conditions developed especially for the coupling of iodide 5 with vinylboronate esters 3c were highly inefficient (Table 1, Entry 1), resulting in a low yield of the desired product 13.…”

Stereoselective Construction of (E,Z)‐1,3‐Dienes and Its Application in Natural Product Synthesis

“…[85] Later, based on the selectivity problems raised by these total syntheses, a methodology for reductive dimerisation was developed that used electron-deficient terminal iodoalkenes and polyenes. [86] In a second generation synthesis, a Heck reaction instead of a Sonogashira cross-coupling reaction (see section 2.10) was applied by Kirschning, where key fragments 96 and 97 were joined to achieve the synthesis of thuggacin derivatives (Scheme 35). [87] Selecting the Heck reaction over the Sonogashira coupling was driven by difficulties found during a C13-C14 alkyne selective reduction.…”