Studies On The Radical Addition And C-H Functionalization-Based Reactions Involving Allenes

Allenes are a class of compounds containing the unique cumulative diene structural units with high reactivity. Much effort has already been made on the radical addition and transition metal-catalyzed reaction of allenes in our group. Based on these studies, this dissertation focused on the radical addition of allene-enes and transition metal-catalyzed C-H bond functionalization involving allenes. Part I. The radical addition of allenes and its application1. On the basis of the previous reports of our group on radical addition of allenes, we have demonstrated a mild, efficient, and non-toxic radical initiator, cheap and readily available zinc powder conbined with HOAc, for the radical addition-cyclization reaction of allene-enes with perfluoroalkyl iodides. The reaction was the first example in an "alkene-to-allene" fashion, affording exo-cyclization products. Utilizing TBAF-promoted dehydroiodination reactions, the products could be converted to heterocyclopentanes with the exocyclic allene moiety conveniently. Furthermore, the radical initiator Zn-HOAc may be applied in the radical addition reactions of perfluoroalkyl iodides with alkenes, alkynes, and allenes.2. Using the literature procedures developed by Dr. Zhichao Ma from our group, the products formed from the radical addition of alkynes and perfluoroalkyl iodides could be transferred to4-electron-withdrawing group substituted-2,3-allenols conveniently, which show unique chemical properties. Herein, we have developed the migrative oxidation of such types of allenes in the presence of NaI and TBSC1affording α,β-unsaturated aldehydes. Furthermore, control experiments indicated that the reactions were promoted by the in-situ formed HI and proceeded a unique C=C bond migrative oxidation. Part Ⅱ. The Rh(III)-catalyzed reactions of allenes based on the C-H functionalization.3. The reports on the reactions of allenes based on C-H functionalization are very limited. Herein, we have developed the Rh(Ⅲ)-catalyzed stepwise ortho-allylation of N-methoxybenzamides with poly-substituted allenes. This C-H functionalization involving allenes is conducted under very mild conditions (-20℃or rt), compatible with ambient air and moisture, and can be applied to terminal or internal allenes with different synthetically attractive functional groups. Monoallyaltion and step-wise diallylation products could be smoothly afforded. Furthermore, highly efficient axial chirality transfer has been realized yielding optically active lactones.4. After that, we have developed the Rh(Ⅲ)-catalyzed Heck-type cross-coupling reaction of N-methoxybenzamides with silylallenes under mild conditions. The methoxy group in the substrates acts as an intramolecular oxidant. Due to the regeneration of the allenic structure, the final products may further be manipulated showing the potentials in organic synthesis.5. Transition metal-catalyzed coupling-cyclization reactions of allenes with a nucleophilic functionality in the presence of organic halides have been proven to be a powerful and efficient tool for constructions of C-C bonds forming cyclic compounds. Herein, we have realized such a coupling-cyclization reaction of2,3-allenols and arenes via C-H bond functionalization. The oxygen in the air has been proven to be an efficient oxidant for promoting this reaction. Highly efficient axial-to-center chirality transfer has been observed. The detailed control experiments indicated that the reaction proceeded in a sequential "C-H metallation-cyclization of allenol-reductive elimination-oxidative regeneration of the transition metal catalyst". Highly efficient axial-to-center chirality transfer has been observed affording the optically active dihydrofuran derivatives.