Amine, enamine/imine, or enamide moieties, as are accessible by hydroamination or -amidation reactions, are widely encountered in the scaffolds of natural products or synthetic drugs (Figure 1). Monomorine is one of the first natural products that became accessible by a synthetic sequence involving a hydroamination step. 2

The influence of the electronegativity of the ligands Y (F, Cl, Br, I, OH, NH2, CH3, H) on the strength of the σ*-aromatic effect in gem-disubstituted 1H-Phosphirenium cations and substituted 3-silacyclopropenes has been investigated with ab initio theory. Phosphorus and silicon provide a low lying p-type σ*-orbital antibonding to the ligands Y. This interacts with the ring double bond analogously to a third p-orbital in a 2π Hückel system. These systems have been compared to the analogous saturated rings. Calculations at the RHF/6-31G* and MP4/6-31+G* levels, NBO analyses of the effect of the ligands Y and comparisons of the relative stabilities of the saturated and unsaturated compounds suggest a weak but significant σ*-aromatic effect dependent on the electronegativity of Y.

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Organophosphorus Compounds, 511). – Phosphatriafulvenes – Phosphaalkenes with Inverse Electron Density2) Peterson olefination of the sterically hindered cyclopropenones 1 with the lithium phosphides 2 yields the so far unknown phophatriafulvenes 3 and 4, which possess inverse electron densities. They are characterized by transition metal complex formation (→7, 8). Acylation of 3a with the carboxylic acid chlorides 11 leads to a great variety of P‐acylphosphatriafulvenes 13a‐s. They partly dimerize under formation of the 1,3‐diphosphacyclobutanes 13 ⇌ 14.

The (diazoalky1)phosphanes 4a-e undergo [4 + 13cycloaddition reactions with the tetrahalo-orthobenzoquinones 5a,b to furnish the previously unknown (diazoa1kyl)phosphoranes 6a-h. The structure of product 6h has been investigated by Xray crystallography.