[structure: see text] A versatile stepwise synthetic approach to cofacial bis-porphyrin species with calix[4]arene spacers has been designed. The three examples described demonstrate that the method allows selection, in a tailor-made fashion, of the calix[4]arene conformation, the type of functionalization of the calixarene rims, and the anchoring point of the chromophores on the calix[4]arene spacer.

Based on the efficient combination of calixarene spacers and acetylenic porphyrin derivatives, a new generation of cofacial bis-porphyrins has been synthesized. The first crystal structure of a cofacial bis-porphyrin-calixarene conjugate is reported. Their unique architectural features, analogous to those of pac-man-type bis-porphyrins, allow these calixarene-porphyrin conjugates to adapt their shape to the size of bidentate guests, such as diazabicyclo[2.2.2]octane (dabco) and 1,4-pyrazine. The predefined, cofacial arrangement of the porphyrin moieties observed in the solid state and in solution results in extremely high affinities (in the range of 10(9) M(-1)) for these guests. The 1,3-alternate calixarene conformations afford "open-mouth" pac-man structures whose ability to bite on nitrogen bidentates depends on their functionalization. A cone conformer provides a much more flexible structure that exhibits the highest affinity for dabco and pyrazine.

A straightforward synthetic route to enantiopure spiro[indole-3,3'-indolizidines] is reported. The key step is a Lewis acid promoted cyclization of a Na-tosyltryptophanol-derived oxazolopiperidone lactam in the presence of Et3SiH.