Evidence is presented for assignment of structure and configuration I to dehydrothalicarpine, a new dehydroaporphine alkaloid isolated from the roots of Thalictrum dasycarpum Fisch. and Lall. Elementary analysis of the alkaloid and its dimethiodide and spectral data supported a C41H46N2O8 molecular formula. Sodium-liquid ammonia cleavage yielded 6′-hydroxylaudanosine (III) and 2,10-dimethoxydehydroaporphine (IV). The 2,10- dimethoxydibenzo[de,g]quinolin-7-one (VII) and 1,2,10-trimethoxydibenzo[de,g]quinolin-7-one (VIII) structures were proposed for two minor products isolated from the sodium-liquid ammonia reaction mixture. Catalytic hydrogenation of dehydrothalicarpine (I) gave thalicarpine (II). A formal total synthesis was achieved by a route which involved oxidation of thalicarpine with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to dehydrothalicarpine. © 1968, American Chemical Society. All rights reserved.