Direct, Sequential, and Stereoselective Alkynylation of C,C‐Dibromophosphaalkenes

Abstract

The first direct alkynylation of C,C-dibromophosphaalkenes by a reaction with sulfonylacetylenes is reported. Alkynylation proceeds selectively in the trans position relative to the P substituent to afford bromoethynylphosphaalkenes. Owing to the absence of transition metals in the procedure, the previously observed conversion of dibromophosphaalkenes into phosphaalkynes through the phosphorus analog of the Fritsch-Buttenberg-Wiechell rearrangement is thus suppressed. The bromoethynylphosphaalkenes can subsequently be converted to C,C-diacetylenic, cross-conjugated phosphaalkenes by following a Sonogashira coupling protocol in good overall yields. By using the newly described method, full control over the stereochemistry at the P=C double bond is achieved. The substrate scope of this reaction is demonstrated for different dibromophosphaalkenes as well as different sulfonylacetylenes.

Palladium-Catalyzed Arylation of a Sterically Demandinggem-Dibromophosphaethene

“…However, the scope of synthetically possible structures remains limited because the substrates must favor generation of the P=C unit. Metalated phosphaethenes can be used to install the conjugated structures into the P=C moieties, although connecting the π‐electron system with the sp 2 carbon of the phosphaethene requires a suitable metalated phosphaethene (Scheme a, ii) …”

Stereoselective Catalytic Synthesis of Alkynylated Phosphaethenes Leading to Activation‐Free Gold Catalysis

“…In comparable previous works, Ott and co‐workers intensively studied various alkynyl‐substituted phosphaethenes for the development of π‐extended phosphaethene derivatives . In a study of alkynyl‐substituted phosphaethenes, Ott et al found that the nucleophilic substitution reaction of bromophosphaethenyllithium [Mes*P=C(Br)Li] with sulfonylacetylenes afforded the corresponding 2‐bromo‐2‐alkynyl‐1‐phosphaethenes [Mes*P=C(Br)C≡CR], which underwent subsequent transformation and redox analyses , . In this work we have demonstrated an efficient catalytic process for the synthesis of various alkynyl‐substituted 2‐bromo‐1‐phosphaethenes by using 1 .…”

1‐Phospha‐Butadienes and 1H‐Phospholes via Alkynylation of Acetylenic Phosphaalkenes

“…In our previously reported synthesis of (di‐)acetylenic phosphaalkenes ( F , G ), [15] we observed during prolonged reaction times, excess of catalyst and acetylene reagent the formation of a minor side product characterized by shielded resonances in the 31 P NMR, which remained elusive at that time. (Scheme 1) In this work, we elaborate on the formation of this side product, the substrate scope of this unprecedented reactivity, and follow‐up chemistry to give highly substituted phosphole (oxides) as valuable molecular building blocks for opto‐electronic materials.…”

“…The angles around the phosphaalkene show the larger impact of the heteroatoms lone pair resulting in a C1-P1-C19 angle of close to 100°. The angles at the C-terminus (C19) are 123.20 (15) and 119.46(14)°, towards the cis and trans substituent, respectively, showing the slight deviation from an ideally sp 2 hybridized carbon C19. (Figure 2) Scheme 1.…”