ChemInform Abstract: The Stereochemistry of Addition of Trialkylammonium and Pyridinium Tetrafluoroborate Salts to Activated Acetylenes. Preparation of Novel Dienophiles for Diels‐Alder Reactions.

Abstract The reactions of the trialkylammonium and pyridinium tetrafluoroborate salts (I), (V), (VIII) with activated acetylenes (II) to give E‐ and/or Z‐isomeric salts (III)/(IV), (VI)/(VII), or (IX), resp., show an unusual stereochemical dependence upon steric factors, solvents, and the nature of the activating group.