SureChem provides structure-searchable access to a database of over 9 million unique compounds extracted from US, European WO patents and Medline records, including prophetic and excluded compounds and other structures not covered by manually constructed databases.  

The database allows exact, substructure and structural similarity searching and is updated a week after new patents are published.  Additionally, Boolean searches can be conducted on by chemical name, title, claims, claims chemical search.  Answers can be filtered on assignee, date and keyword.

Check out the other useful free of charge chemical information resources.