A novel thermal rearrangement of allenic imidothioates. Formation of iminocyclobutenes

Allenic imidothioates, H2CCC(Ph)C(SMe)NR (R = Me, t-Bu, Ph) have been obtained in good yields by reaction of 1,3-dilithiated 1-(2-propynyl)benzene with isothiocyanates and successive addition of t-butyl alcohol and methyl iodide. Heating the imidothioates at ∼120 °C gave an iminocyclobutene as the only isolated product (if R = t-Bu), a ∼4:6 mixture of a 2,3-dihydropyridine and an iminocyclobutene (if R = Me) or a 3:1 mixture of a quinoline and an iminocyclobutene (if R = Ph).