Reduction Behavior of Anisyl‐substituted P‐Ferrocenyl Phospholes

Abstract

P‐Ferrocenylphospholes with differing substituents in α‐position have been synthesized and their identity and purity was confirmed using multinuclear NMR spectroscopy, MS, elemental analysis and single crystal X‐ray diffraction. Furthermore, the redox properties have been explored with electrochemical measurements. Transferring the reduction to a preparative scale using lithium leads to reductive P−C bond cleavage furnishing the corresponding phospholide which has been transformed to P‐tert‐butyl substituted phosphole. In addition to phospholide formation reductive demethoxylation with transformation of the anisyl substituent to its phenyl analog was observed. For comparison analogous reactions have been explored for the respective P‐phenylphospholes which show a different reactivity.

Phospholanes via Twofold C‐H‐Addition to Phospholes

“…We started with the phosphole's α-position and introduced the p-anisyl substituent which had proven to be quite sensitive towards comparable reaction conditions. [18] Remarkably, phospholane 2 c was obtained from 1 c in 64% yield without compromising the integrity of the anisyl substituents. As an obvious further development we were curious about varying the substituent adjacent to the phosphorus atom which is known to have a substantial electronic and steric impact.…”

“…Given the stereospecificity of the here reported cyclization involving four stereogenic centers we were wondering how the stereochemical outcome would be affected by switching from an achiral symmetrically substituted phosphole as starting material to an unsymmetrically substituted phosphole with a P-stereogenic center. Starting from such a phosphole 1 asym reported only recently, [18] the addition of DMSO can be accomplished directly from 1 asym in the presence of a base. Alternatively, its silylated precursor 1 asym -TMS can be used directly in DMSO solution with in-situ generation of a strongly basic anionic intermediate upon desilylation with KOTMS (scheme 4).…”