New P‐ligands: The aromaticity and reactivity of 2,4,6‐trialkylphenylphospholes

A further member of 2,4,6‐trialkyl‐phenyl‐phos‐pholes, the ditertbutylmethylphenyl derivative ( 1c ) was characterized by Bird index and by the sum of angles at the phosphorus atom to describe the flattening of the P‐pyramid. Both numbers suggested a slight aromaticity. The reaction of arylphospholes with phosphorus tribromide was extended to phosphole 1c leading this occasion, after further steps, to the mixture of 3‐ and 2‐substituted products ( 3c‐1 and 3c‐2 , respectively). A triisopropylphenyl‐2H‐phosphole ( 4 ) formed by sigmatropic rearrangement was utilized in the preparation of new 1‐phosphanorbornene derivatives, such as sulfide 6 and hemi‐oxides 8‐1 and 8‐2 . Further oxidation of the latter species ( 8‐1 and 8‐2 ) led to the decomposition of the dimeric structure ( 11 ). 4 could also be trapped by benzaldehyde to afford the oxaphosphanorbornene ( 10 ) as one diastereomer. Finally, the reversible formation of 2H‐phosphole 4 from 1H‐phosphole 1a at 150°C was proved. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:104–222, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20077