Molecular wires of the oligophenyleneethynylene (OPE)‐type are potentially rigid entities. The idea of the work reported herein was to replace some, not all, of the phenylene moieties with ferrocene units, thereby introducing limited conformational flexibility with the ferrocene units acting as hinges as a consequence of the facile rotation around the Cp–Fe–Cp axis. In this context, the syntheses of a number of 1,1′‐diaryl‐disubstituted ferrocene building blocks are described. The new terminal diynes 22 and 24 were used to construct the first representatives of ferrocene‐based molecular wires with three ferrocene hinges. The study includes an X‐ray structure analysis of the thiophene‐based diyne 24 as well as cyclovoltammetric analyses of a number of the compounds prepared.

Abstract5-Dialkylamino-4-pyrrolin-3-ones, available from cyclocondensation of amidines with dimethyl acetylenedicarboxylate (DMAD) undergo rapid singlet oxygenation to give highly functionalized ureas by way of a 1,2-dioxetane cleavage of the initially formed [2+2] cycloadducts. These latter compounds undergo cyclization to 2-oxazolidinones in MeOH. Catalytic hydrogenation of the ureas in EtOAc gives 2-oxazolinones. The DBU-DMAD adduct undergoes photooxygenation by an entirely different pathway to give a large ring heterocycle.The reactions of enamines with singlet oxygen have been extensively studied and the mechanisms involved elucidated. 1-8 In these reactions it has been shown that singlet oxygen combines with enamines by way of an electron transfer or charge transfer mechanism to 1,2-dioxetanes before the latter collapse to carbonyl fragments. Exocyclic enaminoketones and lactones have been reported by Wasserman and Ives to react with 1 O 2 to give 1,2-diones, presumably by way of a 1,2-dioxetane. 9-11 We have extensively studied the singlet oxygenations of the C=N containing compounds in the past and found that by contrast to enaminoketones, α-oximinoketones undergo in the presence of base oxidative C-C cleavage to give esters and carboxylic acids. 12-16 We recently reported the synthesis of 5-dialkylamino-4-pyrrolin-3-ones of the type 3 through a cyclocondensation of amidines with dimethyl acetylenedicarboxylate (DMAD). 17 We also showed that the 4-demethyl analog serves as an excellent precursor of 2-acyltetramic acids, a naturally occurring class of antibiotics and antitumor agents 18 and now report the singlet oxygenations of these compounds.Singlet oxygenations of the enaminoketones (or vinylogous amides) 4 at -78 °C in CH 2 Cl 2 using a high-pressure sodium lamp and tetraphenylporphyrin as sensitizer proceeded rapidly, resulting in quantitative formation of a single product in each case. Based on 1 H and 13 C NMR, as well as elemental analysis, MS spectra and FT-IR data, the products were identified as the vinylogous ureas of the type 6 (Table 1). § This paper is dedicated to Professor Dieter Kaufmann on the occasion of his 60 th birthday.ierden@sfsu.edu. ¥ Authors to whom correspondence regarding the X-ray crystallography should be addressed. The urea structure 6c was further confirmed by X-ray crystallography (Fig.1, Supporting Information). NIH Public AccessUreas 6 underwent cyclization to the 2-oxazolidinones 9 when stirred in MeOH at room temperature. Alternatively, when the photooxygenations of 4a and 4c were conducted in methanol solution instead of CH 2 Cl 2 , the corresponding ureas immediately underwent cyclization to the 2-oxazolidinone derivatives 9a and 9c, respectively. Scheme 2 depicts the mechanism that appears to be plausible for the intramolecular cyclization pathway in the presence of methanol.Upon catalytic hydrogenation of the ureas in an aprotic solvent such as ethyl acetate, the sole products that were obtained after chromatography on silicagel were the 4-oxazolin-2-ones 11a-c ...

The title compound, C16H18O2P2, possesses two stereogenic P atoms and shows a distorted s–cis conformation of each O=P—C=C moiety. This has been suggested on the basis of the stereochemical result of 1,3-dipolar cyclo­additions with nitro­nes and is now confirmed by the present crystal structure analysis. There are two crystallographically independent molecules in the asymmetric unit.