The triptycene-substituted [3]- and [4]helicenes 1 and 2 were examined as possible molecular versions of mechanical ratchets, where the triptycene serves as the ratchet wheel and the helicenes as pawl and spring. The syntheses of 1 and 2b are described. 1H NMR was employed to examine rotation around the triptycene/helicene single bond; at 20 °C rotation is frozen for both 1 and 2b, but the NMR of 1 revealed a plane of symmetry, indicating that 1 cannot function as a unidirectional ratchet. In contrast, NMR revealed that, like a ratchet, triptycyl[4]helicene 2b lacks the symmetry of 1 and has a barrier to rotation of 24.5 kcal/mol, but spin polarization transfer NMR experiments indicated the triptycene in 2b nonetheless rotates equally in both directions. That outcome is rationalized from the standpoint of thermodynamics.

COMMUNICATIONS tural feature of these (TMPDO),TCNE arrays is rectangular four-site 0 -C binding at the TCNE olefinic carbon atoms, which appear to interact through their K* lobes. The topological requirement for DA complexation at the N-oxide center is more flexible, allowing the formation of both ladder and web (crosslinked ladder) DA arrays in the (TMPDO),TCNE crystals as the N-0-C angle flexes. TMPDO (2.58 g, 69%, m.p. 498 K (493 K 1221) was prepared by treatment of 2,3,5,6-tetramethylpyrazine (2.95 g, Aldrich) in CH,CI, (50 mL) with potassium peroxomonosulfate (66.6 g, 5 equiv; OXONE, Aldrich) in H,O (400 mL) with vigorous stirring at 298 K for 24 h. TCNE (Aldrich) was purified by multiple sublimation (373 K, 0.05 mmHg) through activated charcoal. Conditions for the Benesi-Hildebrand analysis: [TMPDO] = 1 . 9 0 m~; [TCNE] =18.7, 34.0, 51.1, 66.4, 75.7, and 9 0 . 6 m~. Purple crystals of (TMPDO),TCNE were prepared by cooling a mixture of TMPDO ( 4 0 m~) and TCNE ( 2 0 m~) in CH,CN to 253 K for 2-5 h. Red prismatic crystals of (TMPDO),TCNE were prepared analogously, after 2-3 d crystallization. Crystal X-ray diffraction was performed on a Siemens SMART diffractometer with CCD area detection at 293 (purple (111) and 173 K (red 1131) with monochromatic Mo,.radiation ( A = 0.71073 8,). Solution and refinement (against were performed with SHELXTL. No absorption correction was employed. Hydrogen atoms were placed in calculated positions (0.95 8, from the methyl carbon atom with tetrahedral angles). They were given torsional freedom and their thermal parameters were set to 1.2 x Oc, of the bonded carbon atom. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-100438. Copies of the data can be obtained free of charge on application to ). Powder Cu,. X-ray spectra were obtained on a Rigaku powder diffractometer. Experimental Section

The synthesis of a series of N,N'-disubstituted indazolone derivatives starting from methyl anthranilates is presented. This general approach features a novel and easy way for access to the target N-heterocycles by formation of a new N-N single bond. The key cyclization step embraces the formation of an N-acylnitrenium intermediate, mediated by the hypervalent iodine reagent PIFA, and its succeeding intramolecular trapping by the amine moiety under rather mild experimental conditions.

The hypervalent iodine reagent PIFA promotes the intramolecular electrophilic cyclization of easily accessible alkynylamides and alkynyl carboxylic acids, leading to the formation of pyrrolidinone and lactone skeletons, respectively, in a very efficient way. A synthetic study and a mechanistic proposal for these transformations are presented.

Dedicated to the memory of our colleague and friend Prof. Marcial Moreno-Mañas. Abstract:The Suzuki biaryl coupling of a range of electronically dissimilar arylboronic acids and aryl bromides is performed in neat water with excellent to quantitative yields by means of a new CNCpincer palladium catalyst that is soluble in water due to its para-carboxy group. Extremely high turnover numbers and frequencies combined with a remarkable robustness allow an effective catalyst reuse in sustainable conditions.