2,4,6‐Trialkylphenyl‐2H‐phospholes from slightly aromatic 1H‐phospholes and their use in [4 + 2] cycloaddition reactions

Abstract

ABSTRACT:1- (2,4,

The Continuing Development of the Chemistry of Phospholes

“…It was also noted in the new study [45,46] that the dimerization was reversible; heating 99a with tolane at 150° C regenerated the (equilibrating) phospholes 96a and 98a and the former then underwent the cycloaddition reaction with 96a. However, when the Psubstituent was the more bulky 2,4,6-tri-t-butylphenyl group, the sigmatropic rearrangement of the P-substituent no longer took place.…”

“…The initially formed product is a 2H-phosphole that ordinarily leads to a dimeric product under the reaction conditions, or is trapped in situ b y dienophiles in a Diels-Alder reaction. A new example of this chemistry is provided by a study of the behavior of sterically-demanding substituents at phosphorus [45,46]. As will be discussed in Section 8, with groups of the size of 2,4-di-t-butyl-6-methylphenyl and 2,4,6-tri-isopropylphenyl, aromatic character in the phosphole ring is increased, but such phospholes (9 5 a and 9 5 b ) undergo the usual rearrangement at 150° C to give the corresponding 2H-phospholes 96a and 96b, trapped by tolane that was included in the reaction mixture to form Diels-Alder adducts 97a and 97b (Equation 32).…”

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

“…• C, a complex mixture was obtained with phosphole oxide dimer 12 as the main component [12]. Formation of 7-phosphanorbornene 12 can be explained by assuming that the bis(phosphine oxide) 11 is not stable and hence is decomposed to the corresponding phosphole oxide that is dimerized instantly (Scheme 3).…”

“…5). Intermediate 4 also dimerizes leading to the isomers of 1,2-diphosphanorbornene derivative 7 (Scheme 2) [12]. Trapped product 5 has now been identified as its P-sulfide (6), and the isomers of dimer 7 have been converted to monoxides 8-1 and 8-2 (Scheme 2).…”

“…The synthesis, properties, and reactivity of 2,4,6-trialkylphenylphospholes were described in earlier publications [1][2][3][7][8][9][10][11][12]. In this paper, the recent findings of ours on the physical and chemical properties of trialkylphenylphospholes are discussed.…”