Stereochemical Behavior of Pairs of P‐stereogenic Phosphanyl Groups at the Dimethylxanthene Backbone

Abstract

The P-stereogenic bis(phosphanes) 7 and 9, featuring pairs of P(Mes)-ethynyl or vinyl substituents at the dimethyl xanthene backbone show rather low barriers of stereochemical inversion at phosphorus. π-Conjugative effects are probably causing these low inversion barriers. Compound 7 reacted with B(C 6 F 5 ) 3 to form the ninemembered heterocyclic product 10, featuring a [P]À C�CÀ B-(C 6 F 5 ) 3 substituent. Compound 7 was converted to the bis[P-(Mes)vinyl] xanthene derivative 9, which gave the zwitterionic P(H)(Mes)À CH=CHÀ B(C 6 F 5 ) 3 containing product 16 upon treatment with B(C 6 F 5 ) 3 . Thermally induced epimerization barriers at phosphorus of ca. 20 to 27 kcal mol À 1 were calculated by DFT for the alkenyl-and alkynyl-P derived systems 6 to 9, 15 and 16 and experimentally determined for the examples 7 and 16.

Reactivity of Primary Phosphines and Primary Phosphine Sulfides towards Imines

“…The number of products is a consequence of the formation of diastereomers after P−H bond addition. Phosphine inversion barriers are determined to be between 132 and 203 kJ/mol, [24,25] typically not amenable to inversion at room temperature [26] . Therefore, two chiral centres are formed in 2° products 1 and three in 3° products 2 (Figure 1b).…”

“…Phosphine inversion barriers are determined to be between 132 and 203 kJ/mol, [24,25] typically not amenable to inversion at room temperature. [26] Therefore, two chiral centres are formed in 2°p roducts 1 and three in 3°products 2 (Figure 1b). The two 2°p hosphine signals correspond to the enantiomer pairs (S c , S p )/ (R C , R P ) and (S c , R P )/(R C, S P ) in an approximate 1 : 1 ratio.…”