Small molecules that induce or stabilize the association of macromolecules have proven to be useful effecters of a wide variety of biological processes. To date, all examples of such chemical inducers of dimerization have involved known ligands to well-characterized proteins. The generality of this approach could be broadened by enabling the discovery of heterodimerizers that target known macromolecules having no established ligand, or heterodimerizers that produce a novel biologic response in screens having no predetermined macromolecular target. Toward this end, we report the construction of a diversified library of synthetic heterodimerizers consisting of an invariant ligand that targets the FK506-binding protein (AP1867) attached to 320 substituted tetrahydrooxazepines (THOXs). The THOX components were generated by a combination of liquid- and solid-phase procedures employing sequential Mitsonobu displacements to join two structurally diversified olefin-containing monomers, followed by ruthenium-mediated olefin metathesis to effect closure of the seven-membered ring. The 320 resin-bound THOX ligands were coupled in parallel to AP1867, and the products were released from the resin to yield candidate heterodimerizers in sufficient yield and purity to be used directly in biologic testing. A representative panel of 25 candidate heterodimerizers were tested for their ability to pass through the membrane of human fibrosarcoma cells, and all were found to possess activity in this tissue culture system. These studies pave the way for further studies aimed at using small-molecule inducers of heterodimerization to effect novel biological responses in intact cells.