Electron‐Rich Aromatic 1,3‐Heterophospholes – Recent Syntheses and Impact of High Electron Density at σ²P on the Reactivity

Abstract

This account reviews recent syntheses, properties, and the reactivity of electron‐rich aromatic 1,3‐heterophospholes, with the focus on benzazaphospholes, but also with inclusion of 1,2,4‐diazaphospholes containing the N–C=P–C motif and related O‐ and S‐containing heterocycles. Effects of the high electron density at phosphorus, a consequence of the position of the lone‐pair donating nitrogen atom in conjugation with dicoordinated (σ2) phosphorus and of the absence of P–N bonds, are illuminated by comparison of selected properties and reactions with those of less electron‐rich heterophospholes and phosphinines. Particular features of the electron‐rich heterocycles are CH‐lithiations of the P=CH fragment by tBuLi without addition at the P=C double bond in polar media, occurrence of inverse addition besides normal addition in less polar solutions, P‐alkylation and catalytic P‐arylation, and – last but not least – the avoidance of σ‐coordination of non‐zerovalent d10 transition metals within the ring plane in favor of μ2‐P and/or tilted η1‐P coordination.

Dual Reactivity of 3a,6a-Diaza-1,4-diphosphapentalene: π-Donor versus n-Donor

“…have been described in the literature because azaphospholes have poor donor properties and easily enter into cycloaddition reactions . Possible candidates for the formation of complexes with organic π-acceptors could be electron-rich 1,3-azaphospholes with high electron density at σ 2 P . However, there is no evidence of such reactions.…”

From a 2,1‐Benzazaarsole to Elusive 1‐Arsanaphthalenes in One Step

“…The chemistry of various synthetically accessible aromatic heterocycles containing heavier Group 15 elements, insteado ft he "classical" nitrogen-based ones, is fairly dominated by the unsaturated organophosphorus compounds. [1][2][3][4][5] Despite recent progress involvingthe heavier congener arsenic, [6][7][8][9][10][11][12] many relatively trivial arsenic heterocycless till remain elusive despitee xhibiting remarkable physical-chemical properties. [1,13] For example,a nd in contrast to arsinine reported by Ashe [14] and 9arsaanthracene independently synthesized by Jutzi [15] and Bickelhaupt, [16] structurally characterized1-arsanaphthalenes (i.e.…”

Chemistry of α‐Phosphanyl α‐Amino Acids

“…After early attempts with PhLi and EtLi failed to lithiate 11 (Me) or to add at the P=C bond of 1,2‐disubstituted benzazaphospholes in Et 2 O,[44a] no other RLi reagents than t BuLi were probed in the lithiation of these heterocycles. The recently found non‐polar conditions and substituent effects, favoring additions at their P=C‐bond,, might open ways to extend the scope of the addition route to other than P‐ tert ‐butyl‐substituted benzo‐fused phosphaprolines.…”