Ditopic molecules in the form of linear reaction templates have been used to construct ladder-like hydrocarbons known as [n]-ladderanes (n=3,5). The templates assemble and position reactant molecules in the solid state by way of hydrogen bonds for [2+2] photodimerization. The products, which are based on recently identified naturally occurring frameworks, form stereospecifically, in gram quantities, and in quantitative yield. The control of reactivity achieved using linear templates provides a basis for the development of molecular tools, termed assemblers, that could be used to manufacture, with atomic-level precision, a wide range of products (e.g. molecular nanostructures) with unique properties.