Chemical Synthesis Database (ChemSynthesis) is a collection over 40,000 compounds with citations to their synthesis. Each record also includes physical properties like density, melting point, and boiling point. ChemSynthesis is searchable by chemical name, CAS registry number, molecular formula, InChiKey, smiles, and journal title. It also has structure search capability.
From the Royal Society of Chemistry, SyntheticPages is a database of synthetic procedures. It contains practical and reliable organic, organometallic, and inorganic chemical synthesis, reactions, and procedures. SyntheticPages is updated continuously, fully searchable, and freely available. Synthetic chemists who wish to contribute must register.
This site contains the complete contents of the volumes of Organic Syntheses from John Wiley & Sons, Inc. It is searchable by text or by structure and browsable by reaction type.