Versatile Reactivity of the Germene Mes₂GeCR₂ toward Esters and Related Carbonyl Derivatives

Abstract

Dimesitylfluorenylidenegermane, Mes 2 GedCR 2 (1; Mes ) 2,4,6-trimethylphenyl, CR 2 ) fluorenylidene), undergoes a [2 + 4] cycloaddition with the CdCCdO system of R-ethylenic esters such as methyl acrylate, dimethyl maleate and dimethyl fumarate, and diethyl fumarate, leading to the 1,2-oxagerma-5-cyclohexenes 2 and 3a,b, respectively. With diethyl oxalate, maleic anhydride, and cyclopent-2-ene-1,3-dione [2 + 2] cycloadditions are observed between the GedC double bond and the carbonyl function, with formation of 1,2-oxagermetanes 4-6, respectively. In the last case, a double [2 + 2] cycloaddition on both CO groups to form a tricyclic compound occurs with excess germene. Germene 1 reacts exclusively by an ene reaction with 2-methyl-1,3-pentadione to give the corresponding (germyloxy)cyclopentenone 8.

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

“…This result is not surprising since a [2+2] cycloaddition between the GeC double bond of germene 1a and one CO double bond of maleic anhydride has previously been observed; in the case of 4-cyclopentene-1,3-dione, a double [2+2] cycloaddition onto both carbonyl groups occurred; these five-membered-ring carbonyl reagents also contain a conjugated system OC−CC.…”

C–H Activation Reactions of a Nucleophilic Palladium Carbene

“…The reaction of carbene 1 with fluorene only occurs with thermal activation, after which it proceeds relatively quickly and produces cleanly the Pd–(η 1 -fluorenyl) product [PC­(H)­P]­Pd­(η 1 -fluorenyl) ( 5 ; eq ) by heterolytic C–H bond cleavage of the substrate. While there are no other crystallographically characterized examples of Pd–(η 1 -fluorenyl) or Pd–(η 5 -fluorenyl) derivatives, some examples of η 1 -fluorenyl (Fl) complexes exist when supported by other metals: Ge (η 1 -Fl); Ga (η 1 -Fl); Mn (η 1 -Fl and η 5 -Fl); Li, Na, K, Cs, Ca, Ba; Zn; Zr; Ti; Mo; Ni; Cu; Au . Examples of indenyl palladium complexes (with variable hapticity: 1, 3, or 5) have been reported …”

Reactivity of a Linear 2‐Germapropadiene with Acids, Ketones, and Amines

“…Subsequently, a second [2+2] cycloaddition affords spiro compound 4 . It is known that germenes and their related compounds undergo formal [2+2] reactions with aldehydes and ketones leading to four‐membered heterocycles [2h,3b,8] . In 2‐germapropadiene 1 , which contains two C=Ge double bonds, this [2+2] cycloaddition can occur twice.…”