The cascade [1,n]-hydrogen transfer/cyclization, recognized one century ago, has received considerable interest in recent decades and great achievements have been made. This cascade process can functionalize C(sp3)H bonds directly into CC, CN, CO bonds under the catalysis by Lewis acids, Brønsted acids or organocatalysts, and even under thermal conditions. This methodology has shown preeminent power to construct 5- or 6-membered heterocyclic as well as all-carbon rings. In this review, various hydrogen donors and hydrogen acceptors are categorized and discussed.
Abbreviations: Cbz: benzyloxycarbonyl; Cod: 1,5-cyclooctadiene; CSA: camphorsulfonic acid; DCE: 1,1-dichloroethane; DFT: density function theory; DMF: N,N-dimethylformamide; DNBS: 2,4-dinitrobenzenesulfonic acid; DPP: diphenyl phosphate; ERC: electrocyclic ring closure; Fmoc: 9-fluorenylmethoxycarbonyl; HT: hydrogen transfer; IBX: ortho-iodoxybenzoic acid; m-CPBA: meta-chloroperbenzoic acid; MW: microwave; MS: molecular sieves; Pg: protecting group; p-TSA: para-toluenesulfonic acid; r.t.: room temperature; TCE: 1,1,2-trichloroethane; TFA: trifluoroacetic acid; TMS: trimethylsilyl.