Science of Synthesis is the 5th edition of the Houben-Weyl Methods in Organic Chemistry series. It is a highly organized and authoritative collection of authored reviews on organic synthetic methods. Chapters contain experimental procedures, background information, and extensive bibliographies. Its purpose is to provide a direct path through the mass of primary literature on a wide range of organic reactions. The base set (48 volumes, 2000-2010) contains information on over 265,000 reactions and 29,000 experimental procedures. A chemist looking for the present knowledge of a type of synthetic method or class of compounds might start in SoS and follow up with searches for structures/reactions and/or keywords in SciFinder, and for structures/reactions in Reaxys. SoS chapters provide numerous references to the primary journal literature, but these are selective, not comprehensive.
Volume E23 of the Houben-Weyl 4th edition supplementary series (the "E" volumes) is a multivolume structural formula index of reaction products by compound class, but it is not for the faint of heart. Vol. 16 of the earlier base set comprises indexes by experimental procedure and substance class for the 4th edition and E-Series volumes 1-5 and 11 (i.e. through about 1986).