Intramolecular Hydroamination Route to Heterocycles

Abstract

Intramolecular cyclizative hydroamination of unactivated double and triple bonds under inexpensive zinc-based catalysis is reported. The illustrated catalyst shows excellent solubility in most organic solvents, air and moisture stability, low toxicity and is compatible with a variety of polar functional groups such as ethers, amides and hydroxylamines to give products in excellent, often quantitative yields. Thus, dihydropyridones A and B, dihydropyrrole N-oxides C, tetrahydro-oxazepines D, dihydrooxazines and dihydropyrazines are obtained in excellent conversion. The absence of co-catalyst {[PhNMe2H][B(C6F5)4]} led to the formation of exocyclic double bond isomer A as the major product. On the other hand, the ­dihydropyridone B was observed when an equal amount of the co-catalyst was added. Similarly, the intramolecular hydroamination of non-activated alkenes (e.g., 2-methylpent-4-en-1-amine) was also accomplished.