Nucleophilic substitution in benzylic thiophosphinyl and thiophosphonyl chlorides: the contribution of elimination–addition pathways with methylenethioxophosphorane (thiophosphene) intermediates

Abstract

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Preparation, structure, and reactivity of a new heterocyclic system‐1‐thio‐2,8‐diphenyl‐2,5,8‐triaza‐1λ5‐phosphabicyclo[3.3.0]octane

“…Change of the reagents and conditions (CH 2 Cl 2 /reflux, two mol equivalents of Et 3 N/THF, aq NaOH/CCl 4 , BuLi/ THF/‫87מ‬ЊC) resulted in some reactions, but the crude product always consisted of a complex mixture of phosphorus-containing compounds ( 31 P NMR). The attempt to substitute oxygen for sulfur by treating 1a (1, R ‫ס‬ Ph) with P(S)Cl 3 /DMF [3] resulted also in a mixture of products from which 2a could not be isolated. A solution to the problem was derived from our most recent results [4], according to which the previously difficult to prepare bis(2-arylaminoethyl)amines (3) were obtained by exhaustive hydrolysis of triamidates 1.…”

Methylenethioxophosphorane (thiophosphene) intermediates in the reactions of diphenylmethylphosphonamidothioic chlorides with amines. Differences between the elimination–addition mechanisms of nucleophilic substitution for PS and PO substrates

“…11 The Me 2 NH/Et 2 NH rate difference for the P᎐ ᎐ S substrate 5a (k M /k E = 50) is an order of magnitude greater than for the P᎐ ᎐ O substrate 3a (k M /k E = 5) 13 or for the fluorenyl substrate 1 (k M /k E = 4) 7 and its P᎐ ᎐ S counterpart (k M /k E = 4). 11 It is not quite as great as is seen in the S N 2(P) reactions of PhP(S)(NMe 2 )Cl (k M /k E = 200), 15 but the complete selectivity for Me 2 NH in the competition experiment is exactly what would be expected for S N 2(P). 7, 15 The nitro-substituted substrate 5b shows rather less discrimination against Et 2 NH, both in terms of rate of reaction (k M /k E = 21) and competitive product formation (NMe 2 : NEt 2 product ratio 97 : 3), but its behaviour is still hardly supportive of an EA mechanism.…”

Relative Ease of Formation of Alkylidine(oxo and thioxo)phosphorane Intermediates in Nucleophilic Substitution at Phosphonyl and Thiophosphonyl Centres

“…The phenyl phosphonamidothioic chloride PhP(S)(NMe 2 )Cl reacts 200 times faster with Me 2 NH than with Et 2 NH (t 1/2 4 min and 13.5 h with 0.6 mol dm À3 amine in CH 2 Cl 2 at 33 8 8C), 4 and with both amines its reactivity is much less than that of the ¯uorenyl compound 5. Also, in competition experiments using a 1:1 mixture of Me 2 NH and Et 2 NH, the phenyl substrate forms only the product derived from Me 2 NH, 4 whereas the ¯uorenyl substrate 5 gives a substantial amount of the product 7 (R' Et) derived from the less nucleophilic (more hindered) Et 2 NH (Me 2 N:Et 2 N product ratio 5:1). The relative lack of discrimination in the case of the ¯uorenyl compound is consistent with a reactive and sterically accessible thiophosphene intermediate as the product-forming species.…”