Reactions of Germenes with Somepara-Quinones: Formation of a Tricyclic Compound from 1,4-Benzoquinone Undergoing an Unexpected Rearrangement

Abstract

Germenes Mes 2 GedCR 2 1a (Mes = 2,4,6-trimethylphenyl; CR 2 = fluorenylidene) and Mes 2 GedCR 0 2 1b (CR 0 2 =2,7-di-tert-butylfluorenylidene) react with 1,4-benzoquinone and 2,3,5,6-tetramethyl-1,4-benzoquinone to give compounds 3a, 3b, and 5a, containing a 1,4-cyclohexadiene unit as central ring. Upon prolonged storage in diethyl ether or THF solution, compounds 3a and 3b undergo a double 1,3-hydrogen shift, leading to their structural isomers 4a and 4b. Theoretical calculations performed on the model compound H 2 GedCH 2 1H postulate that the first steps of its reaction with 1,4-benzoquinone are a double [2þ2] cycloaddition between the GedC and CdO double bonds, leading to a transient dispiro compound containing two oxagermetane rings, followed by its isomerization to derivative 3H. Between 1a and 9,10anthraquinone, a double [2þ4] cycloaddition is observed involving the oxygens and the ortho-carbon atoms of one adjacent aromatic ring system, to generate the dioxadigermabenzopyrene derivative 2a.

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

“…Whatever the quinone, similar reactions are observed leading to stable spiro compounds with four‐membered oxagermacyclobutane rings. These results confirm the first step of the reaction postulated by calculations for germene and 1,4‐benzoquinone 5. Spiro compounds 2 – 5 do not undergo rearrangement in solution and the formation of five‐ or six‐membered ring derivatives has not been observed.…”

“…For example, [2 + 4] cycloadditions involving the O=C–C=CH unit with naphthoquinone3 and anthraquinone4 and two different types of formal [2 + 3] cycloadditions involving the O=C–CH unit with naphthoquinone,3 1,4‐benzoquinone,5 and 2,3,5,6‐tetramethyl‐1,4‐benzoquinone have been observed 5. Whatever the stoichiometry of the reagents, the final product is formed from two molecules of germene and one of quinone.…”

“…In order to understand the surprising reaction leading to the five‐membered ring oxagermacyclopentanes, DFT calculations have been performed on 1,4‐benzoquinone and the model compound H 2 Ge=CH 2 . They predict that the first step of the reaction leading to I is a double [2 + 2] cycloaddition between the Ge=C and C=O double bonds to give transient dispiro compound II , with two four‐membered oxagermacyclobutane rings, followed by its rearrangement to give the final adduct with five‐membered rings (Scheme ) 5…”

Addition of Aldehydes to Germenes: The Influence of Solvent

“…The residue was purified by preparative thin-layer chromatography (SiO 2 , CHCl 3 ) to give a colorless solid (128 mg, 0.26 mmol, 86%) identified as fluorogermane 6. The spectral data agreed well with the published values 5a ( 1 H NMR chemical shifts, (0.05 ppm; 19 F NMR chemical shifts, (2.5 ppm). 13 A translucent colorless blocklike crystal of C 31 H 31 FGe, approximate dimensions 0.07 mm  0.08 mm  0.11 mm, was used for X-ray crystallographic analysis.…”

“…13 C NMR (C 6 D 6 ): δ 143.45 (fluorenyl C), 143.12 (Mes o-C), 141.03 (Mes p-C), 136.53 (Mes i-C), 135.78 (fluorenyl C), 133.56 (GedC), 129.14 (Mes CH), 126.12 (fluorenyl CH), 124.16 (fluorenyl CH), 121.23 (fluorenyl CH), 120.02 (fluorenyl CH), 24.01 (Mes o-CH 3 ), 21.19 (Mes p-CH 3 ) 19. F NMR (C 6 D 6 ): δ no significant signals observed; À173 (residual 6).…”