Incorporation of Group 14 Elements into Siloxane-Bridged Paracyclophanes cyclo-[p,p‘-Me2SiC6H4EMe2C6H4SiMe2O]2 (E = C, Si, Ge, Sn)

Regio- and stereoselective synthesis of spiropyrrolidine-oxindole and bis-spiropyrrolizidine-oxindole grafted macrocycles through [3 + 2] cycloaddition of azomethine ylides

A convenient and efficient method for the regioselective macrocyclization of triazole bridged spiropyrrolidine-oxindole, and bis-spiropyrrolizidine-oxindole derivatives was accomplished through intra and self-intermolecular [3 + 2] cycloaddition of azomethine ylides. The chalcone isatin precursors 9a-i required for the click reaction were obtained from the reaction of N-alkylazidoisatin 4 and propargyloxy chalcone 8a-i which in turn were obtained by the aldol condensation of propargyloxy salicylaldehyde 6 and substituted methyl ketones 7a-i. The regio- and stereochemical outcome of the cycloadducts were assigned based on 2D NMR and confirmed by single crystal XRD analysis. High efficiency, mild reaction conditions, high regio- and stereoselectivity, atom economy and operational simplicity are the exemplary advantages of the employed macrocyclization procedure.

Synthesis of heteroatomic bridged paracyclophanes

Heteroatomic bridged paracyclophanes were obtained by two independent synthetic approaches. The required precursors consist of para R₂SiCl (R = Me, iPr) substituted aromatic rings (2 and 4). They were subsequently functionalised by using NH₃, [LiPH₂(dme)] or LiAl(PH₂)₄. In the case of the Me-substituted species 2, the reaction with NH₃ directly yielded the Si₂N bridged paracyclophane 5. The Si₂P incorporated derivative 10 was obtained by lithiation of p-C₆H₄(SiiPr₂PH₂)₂ (9) and subsequent salt metathesis with the chlorosilane 4. The second approach involves the use of GaEt₃ in the formation of four membered (GaPn)₂ cycles (Pn = N, P). p-[C₆H₄{SiiPr₂N(H)GaEt₂}₂]₂ (11) and p-[C₆H₄{SiiPr₂P(H)GaEt₂}₂]₂ (12) represent the first examples of stable (GaPn)₂cis isomers as the trans species did not appear in solution. Although 11 and 12 show a similar coordination pattern, they differ in the orientation of the aromatic systems: in the solid structure, 11 adopts a - for paracyclophanes so far unique - T-shape conformation of the phenyl rings, while 12 shows the predominant coplanar orientation. All cyclophanes were characterized by X-ray diffraction, elemental analysis, NMR and IR spectroscopy.

Palladium-catalyzed Si–C bond-forming silylation of aryl iodides with hydrosilanes: an enhanced enantioselective synthesis of silicon-stereogenic silanes by desymmetrization

An enantioselective Pd-catalyzed silicon–carbon bond-forming silylation reaction of aryl iodides with hydrosilanes for the synthesis of silicon-stereogenic silanes has been developed with good enantioselectivity under mild conditions.

Silylations of Arenes with Hydrosilanes: From Transition-Metal-Catalyzed C¢X Bond Cleavage to Environmentally Benign Transition-Metal-Free C¢H Bond Activation

The construction of carbon-silicon bonds is highlighted as an exciting achievement in the field of organosilicon chemistry and green chemistry. Recent developments in this area will enable the sustainable chemical conversion of silicon resources into synthetically useful compounds. Especially, the catalytic silylation through C¢H bond activation without directing groups and hydrogen acceptors is one of the most challenging topics in organic chemistry and green chemistry. These remarkable findings on catalytic silylation can pave the way to a more environmentally benign utilization of earth-abundant silicon-based resources in synthetic chemistry.