{"knowledge_schema": {"broad_category": "Chemistry \u2192 Organic Chemistry \u2192 Stereochemistry and Reaction Mechanisms", "refinement": "This problem involves identifying the correct starting materials for two separate reactions based on the stereochemical outcomes of the products.", "specific_scope": "The focus is on determining which of the given candidates corresponds to the starting materials that yield specific stereoisomers of a compound after reduction with different agents.", "goal": "Select the appropriate starting materials (A and B) that lead to the desired products with the specified stereochemistry."}, "summary": "This problem is rooted in organic chemistry, specifically in the area of stereochemistry and reaction mechanisms. It requires identifying the correct starting materials for two reactions that produce specific stereoisomers of a compound after treatment with different reducing agents. The goal is to analyze the candidates provided and determine which pair of compounds (A and B) will yield the desired products, (R)-4-ethyltetrahydro-2H-pyran-2-one and (S)-4-ethyltetrahydro-2H-pyran-2-one, through the respective reactions."}