Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

Abstract

3-Methylbuta-1,2-dien-1-ylphosphonic acid derivatives (phosphorylallenes) [X2(O=)P–CR=C=CMe2, X = Cl, OMe, NR2, or SAr] undergo intramolecular cyclization into the corresponding 1,2-oxaphospholium ions in the Brønsted superacid TfOH. These cations have been thoroughly studied by means of NMR spectroscopy. The hydrolysis of superacidic solutions of these species afforded cyclic phosphonic acids and other phosphorus-containing compounds. Contrary to Brønsted acids, 3-methylbuta-1,2-dien-1-ylphosphonic dichloride [Cl2(O=)P–HC=C=CMe2] reacted with the Lewis acid AlCl3 in an intermolecular way forming noncyclic intermediates, which were investigated by NMR spectroscopy and DFT calculations. Hydrolysis of these species resulted in the formation of phosphoryl-substituted allyl alcohols and 1,3-butadienes. A strong coordination of the oxygen of the P=O group with AlCl3 prevented the formation of cyclic 1,2-oxaphospholium ions and played a crucial role in the different reactivity of such phosphorylallenes under the action of Brønsted or Lewis acids. Apart from that, the reaction of dichlorophosphorylallenes with arenes and AlCl3 led to products of hydroarylation of the allene system, phosphoryl-substituted alkenes and/or indanes. This is the first example of a Lewis acid-promoted intermolecular hydroarylation of allenes bearing electron-withdrawing substituents. Plausible reaction mechanisms have been proposed on the basis of the investigated reactions, and NMR analysis and DFT studies of the intermediate cationic species.

Accessing Five- and Seven-Membered Phosphorus-Based Heterocycles via Cycloaddition Reactions of Azophosphines

“…27 Given the partial single-bond character of the P-N bond in five-membered rings 4-6, we hypothesised that this bond could be cleaved by certain substrates to yield larger phosphorus-containing heterocycles, by analogy with the aforementioned ring expansion chemistry. 16,17 Reactions of an P-N bond within fivemembered rings has previously been reported with ketones, ketenes, and isocyanates, although in all cases either acyclic or bicyclic structures were observed instead of ring expansion. 28-30 Cummins also reported one example of P-N bond cleavage in an N-heterocyclic iminophosphorane with Ph3SiH, although this resulted in loss of the heterocyclic structure and formation of a Ph3Si-N(R)-H moiety.…”

“…Regioselective synthesis of heterocycles 9 (A) and 10 (B) via the reaction of azophosphines with ethyl 2-butynoate. (17). 9 crystallised with two product molecules in the asymmetric unit; only one is shown here for clarity.…”

“…In 2019, Lozovskiy et al also reported intramolecular ring-expansion by P-N bond cleavage in a fivemembered ring to yield a seven-membered ring. 17 The only prior example of 1,2,5-diazaphosphepine chalcogenides was reported by Barkallah et al, where 2,2'-(phenylphosphoryl)bis(cyclopentan-1-one) (or the sulfur and selenium analogues) was reacted with hydrazine and acetic acid (Figure 1B), although the products were not structurally characterised. 18 Azophosphines are phosphorus-containing analogues of triazenes with the chemical formula ArN=N-PR2, with a trivalent phosphorus centre that can be exploited for further reactivity.…”

“…Single crystal structures of 9 (A) and 10 (B). Selected bond distances (Å): 9 N1-N2 1.4117(18), N2-P1 1.6382(13), C18-C19 1.390(2); 10 N1-N2 1.4103(18), N2-C12 1.286(2), C12-C13 1.452(2), C13-P1 1.7268(17). 9 crystallised with two product molecules in the asymmetric unit; only one is shown here for clarity.…”

Superelectrophilic Activation of Phosphacoumarins towards Weak Nucleophiles via Brønsted Acid Assisted Brønsted Acid Catalysis

“…The reactions of vinyl type carbocations derived from ethynylphosphonates with substituted benzenes in fluorosulfonic acid have been described by Vasil’ev and coworkers [ 21 , 22 ]. Later, the same group reported a series of transformations of 1-(phosphoryl)allenes in superacidic media, which furnished various phosphorus heterocycles [ 23 , 24 , 25 , 26 , 27 ]. Thus far, these are the only known reactions of organophosphorus superelectrophiles.…”