Giuseppe Borsato

Benzocyclotrimers: from the Mills-Nixon effect to gas hosting.

The formal annulation of three bicylic olefins yields a class of molecules termed benzocyclotrimers (BCTs), which have unusual electronic properties. The bonds in the central aromatic ring, for example, alternate in length: rather than resembling a substituted benzene, a BCT instead evokes comparison to a cyclohexatriene. Forty years have passed since the synthesis of heptiptycene, the first BCT, was reported. In the interim, many methods have been developed for preparing tris-bicycloannulated benzenes. More than thirty different BCTs have so far been reported, with a variety of morphological features and properties. Over the same period, yields have increased from just a few percent to almost quantitative conversion. This improvement in synthetic access has expanded interest beyond the original theoretical considerations (bond-length fixation in aromatics) to functional applications (supramolecular scaffolds). In this Account, we describe the evolution of synthetic approaches to BCTs and their derivatives, as well as the applications that are now being explored for these compounds. Early syntheses of BCTs involved chloroolefins treated with butyl lithium. A strained alkyne intermediate was postulated early on, and was indeed trapped in 1981. Subsequent efforts have focused on improving chemoselectivity by mitigating the drastic conditions required for the generation of the alkyne intermediate. Our introduction of Cu(I) to induce lithium-copper exchange was successful in this regard. Further improvement resulted from the use of bicylic bromo(trimethylstannyl)olefins. In an effort to avoid the toxicity of the tin reagents, the Heck reaction and Pd catalysis have been pursued for cyclotrimerizing bicylic bromo- and iodoolefins. Depending on the symmetry of the starting bicylic olefin, two diastereomers can be obtained in the preparation of a BCT: a syn compound with C(3) symmetry and an anti compound with C(s) symmetry. Studying the diastereomeric outcome in a variety of synthetic approaches has yielded valuable insight into the cyclotrimerization reaction. Moreover, highly symmetric compounds, such as a D(3)-symmetric trindane and C(3v)-symmetric sumanene, have been prepared as BCT derivatives. The structure of BCTs offers a versatile three-dimensional scaffold for studying molecular recognition. Like calixarenes, BCTs form complexes with a variety of guest molecules. Recent developments include the trapping of gases in a hydrogen-bonded dimer and the encapsulation of larger molecules within a covalently linked condensation derivative. Future innovations in this fertile research area will likely include highly functionalized curved aromatics, receptors, and sensors.

Synthesis of the syn and anti isomer of 1,4,5,8,9,12-hexahydro-2,3,6,7,10,11-hexamethylidene-1,4:5,8:9,12-trimethano triphenylene and Diels–Alder reactivity of the syn isomer

The title compounds, new members in the class of tris-annelated benzenes with [2.2.1] bicyclic rings, were obtained in high yields by coupling of 2-bromo-3-trimethyltin-5,6-dimethylenenorborn-2-ene with copper(I) 2-thiophenecarboxylate (CuTC). The syn isomer was reacted with 3 equiv. of the dienophiles TCNE, DMAD, PTAD and norbornadiene to afford the corresponding cycloadducts.

Synthesis and evaluation of new chiral diols based on the dicyclopentadiene skeleton

Abstract The resolution by Lipase PS of rac - 5 (from reduction of ketone 6 , obtained from dicyclopentadiene with a new environment-friendly synthesis) gives (2 S )- 5 , which was further reduced to the endo (2 R )- 1a alcohol. The endo (2 S )- 1b alcohol was obtained from camphor with a multistep synthesis. Pinacol couplings of 3a , b , carried out with Mg/Hg or Coreys general procedure respectively, afforded with high diastereoselectivity the C 2 symmetry diols (2 R ,2′ R )- 2a and (2 S ,2′ S )- 2b , with endo oriented OH functions. The enantiogenic power of the endo alcohol (2 R )- 1a and (2 S )- 1b and of the diols (2 R ,2′ R )- 2a and (2 S ,2′ S )- 2b was tested towards the LiAlH 4 reduction of acetophenone. The C 2 symmetry appears to play a fundamental role.

Catalysis Within the Self-Assembled Resorcin[4]arene Hexamer

Abstract In the field of supramolecular catalysis aiming at enzyme mimicking, the self-assembled hydrogen- bonded hexameric capsule of resorcin[4]arene represents in organic solvents one of the largest nanometric supramolecular containers where catalysis takes place with peculiar features. In particular, the confined electron-rich environment of the capsule provides steric as well as electronic interactions with either encapsulated cationic metal catalysts, thus imparting unique catalytic control on both product and substrate selectivity, or with electron poor substrates and intermediates, thus leading to efficient examples of supramolecular organocatalysis in cases ranging from hydrolysis and hydration reactions to C C and C heteroatom bondforming reactions. Capsule exploitation as a nanoreactor to impart new activities and selectivities to known catalysts or as a true nanoorganocatalyst can be also endowed with properties like inhibition by competitive guests that is reminiscent of enzymatic catalysis.

Highly Efficient Synthesis of C3-symmetry O-alkyl Substituted Triphenylene and Related Mannich Derivatives

C 3-Symmetric tris-benzyl-O-substituted hexahydroxytriphenylene (HHTP) was prepared through selective ring opening with DIBAL-H in 48% yield (38% from HHTP in a two-step synthesis) avoiding the use of noxious, expensive and limited market availability reagents, with complete recovery of the undesired Cs co-product that is quantitatively recovered and converted back into HHTP. The C3-symmetric triphenylene product was further functionalized through substitution, deprotection and Mannich condensation reactions affording a series of C3-symmetric functionalized scaffolds in good yields for supramolecular applications.