Synthetics
Grapefruit mercaptan smells intensely like grapefruit juice, even in incredibly small amounts.
Mosciano, Gerard P&F 23, No. 3, 55, (1998): Sulfurous, alliaceous, grapefruit, onion, garlic, tropical and woody
Luebke, William tgsc, (2009): Sulfury aromatic grapefruit naphthyl resinous woody
R C Treatt & Co Ltd: Intense grapefruit top-note
R C Treatt & Co Ltd: Intense grapefruit top-note