Found in blackcurrant bud absolute - responsible for the slightly metallic crushed fruit aspect. Use it in your cassis accords but also try in a white wine note.  Also found in cat urine. 
 
I've sold this one for years, and it's apparently developed such a reputation that some hobby shops have now started selling it🤭. Unlike the SigmaAldrich version sold elswhere (which I rejected for having a rubbery note - if you go to look at the product at Sigma, it's actually only 97-98% pure lol) I get mine made by a specialist in sulfur aromachemistry, and the final product is 99.8% pure. 
 
Dilution wise, 0.1% is plenty. Remember that this is an incredibly powerful material, typically used at 0.001-0.005% of a perfume formula. Shipping dilutions like 1% or even 10% of this material also risks of subtle cross contamination both during shipment and later in your lab, regardless of containment vessel and sealing. Cassis pentanone is a nifty and conniving species, best treated with respect 😹
 
See also Ribenone for an excallent complement to this material