Reactivity of Quinones with Phosphagermaallene Tip(tBu)Ge=C=PMes* Leading to Four‐ and Six‐Membered Heterocycles with an Exocyclic P=C Double Bond

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Abstract
Phosphagermaallene Tip(tBu)Ge=C=PMes* (1) (Tip = 2,4,6‐triisopropylphenyl, Mes* = 2,4,6‐tri‐tert‐butylphenyl) reacts with one equivalent of p‐quinone (1,4‐benzoquinone, 2,3,5,6‐tetramethyl‐1,4‐benzoquinone, 1,4‐naphthoquinone, and 9,10‐anthraquinone) to form spiro 1‐oxa‐2‐germacyclobutane compounds 2–5 with an exocyclic P=C double bond by [2 + 2] cycloaddition between the Ge=C and one of the C=O double bonds. With two equivalents of 1 a double [2 + 2] cycloaddition occurs involving both unsaturated C=O bonds of 1,4‐benzoquinone to give the dispiro compound 6. [2 + 4] Cycloadditions are observed between the Ge=C double bond of 1 and the O=C–C=O unit of an α‐diketone (benzil) and an o‐quinone (9,10‐phenanthrenequinone) to give the corresponding 1,4‐dioxa‐2‐germa‐5‐cyclohexenes 7 and 8.

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