Synthesis of Azaphosphinines by Directed Inverse‐Electron‐Demand Hetero‐Diels–Alder Reactions with Na(OCP)

Abstract

Herein, a straightforward synthetic approach towards azaphosphinines is reported. The synthesis of 1,3- and 1,4-aza-λ -phosphinines as well as 1,2,4-diaza-λ -phosphinines by inverse-electron-demand hetero-Diels-Alder reactions of sodium 2-phosphaethynolate [NaOCP] with triazines and tetrazines is studied. In the case of 1,2,4-triazines a hetero-D.A. reaction was developed, which relies on a new directing-group approach based on the complexation of sodium to form an ionic Do→Na-OCP tether. The first X-ray characterization data for aza-λ -phosphinines as well as the first phosphinine triflates are presented.

Heavier element-containing aromatics of [4n+2]-electron systems

“…In 2018, a variety of azaphosphinines were synthesized by Hansmann by hetero-Diels-Alder reactions with Na(OCP). 254 The reaction of 1,2,4-triazine 4-39-1 with Na(OCP) in THF led to the formation of 1,4-azaphosphinines (6CNP1) or/and 1,3azaphosphinines (6CNP2) (Scheme 4-39). The 31…”

Recent advances in the chemistry of the phosphaethynolate and arsaethynolate anions

“…reactions. 107 The reaction of 1,2,4-triazine ( 118a ) with [Na(dioxane) x ](OCP) resulted in 1,4- ( 119a ) and 1,3-azaphosphinines ( 120a ) in 4 : 1 ratio (Scheme 38) at elevated temperature. 108 However, the effort to improve the reactivity and regioselectivity by using more electron-deficient tetrazine ( 118b ) failed.…”

Understanding the Mechanism of Diels–Alder Reactions with Anionic Dienophiles: A Systematic Comparison of [ECX]− (E = P, As; X = O, S, Se) Anions

“… 6 − 11 Consequently, a plethora of thorough experimental and theoretical studies have been devoted to the properties and reactivity of the [PCO] − anion, underlining that this simple anion has become an important building block, especially in low-coordinate phosphorus chemistry. 12 − 16 On the basis of these investigations, besides nucleophilic substitutions and P – -transfer reactions, 13 , 17 − 22 cycloadditions are also of high importance, in which various P heterocycles can be accessed in a straightforward manner. 12 , 14 , 23 , 24 …”

“… 26 Recent studies reported the synthesis of aza- and diazaphosphabenzenes using tri- and tetrazines along with a phosphaphenolate analogue from methyl coumalate. 15 , 16 Importantly, cycloadditions utilizing the [PCO] − anion can also deliver annulations; for example, the 2-phosphanaphth-3-olate framework has been successfully accessed from phthalazine ( Scheme 1 ). 27 Very recently, this methodology even enabled the construction of “depolymerizable” coordination polymers.…”

“…Later on, Grützmacher and co-workers developed a convenient synthetic route to accessing the sodium salt, Na­[OCP], which is stable as a dioxane adduct at room temperature and even at higher temperature under an inert atmosphere . Besides the sodium cation, further countercations have been tested; however, in practice, the sodium salt remains the most frequently used analogue, especially because of its simple and efficient synthesis in large amounts. − Consequently, a plethora of thorough experimental and theoretical studies have been devoted to the properties and reactivity of the [PCO] − anion, underlining that this simple anion has become an important building block, especially in low-coordinate phosphorus chemistry. − On the basis of these investigations, besides nucleophilic substitutions and P – -transfer reactions, ,− cycloadditions are also of high importance, in which various P heterocycles can be accessed in a straightforward manner. ,,, …”