Phase-transfer catalyzed formation of cyanohydrin ethers and acetates

In the presence of an allylic bromide, aldehydes, but not ketones, react with cyanide ion under phase-transfer catalysis to give cyanohydrin allyl ethers which can be converted to ketones. Other alkylating agents and nucleophiles give different results. Replacing the allylic bromide with acetic anhydride leads to cyanohydrin acetates.