Studies On The Synthesis And Reactions Of Allenes Based On Rh(?)-Catalyzed C-H Bond Activation

Containing the simpliest unique cumulative diene structural units,allenes are highly reactive compounds.Recently,systematical studies on the synthesis of allenes and their nucleophilic addition reactions,electrophilic addition reactions,radical-based reactions,and cyclization reactions have been conducted in our group.On the other hand,C-H activation reactions have become more and more popular since such reactions can avoid the pre-activation of starting materials under mild conditions,tolerate many synthetic useful functional groups,and afford a variety of potentially useful products.Thus,the main fouse of this dissertation is on C-H activation-based allene synthesis and reactions.Part ?.We have demonstrated a Rh(?)-catalyzed C-H functionalization-based formal[4+2+2]cyclization of N-pivaloyloxy benzamides with 1,6-allene-enes forming eight-membered lactams.The reactions occur at room temperature and are compatible with air and moisture with a tolerance of many synthetic useful functional groups.The synthetic applications have been demonstrated.After careful mechanistic studies and DFT calculation,we proposed the reaction mechanism.Part ?.We have developed a Rh(?)-catalyzed C-H bond activation-based reaction of the readily available arenes with sterically congested tertiary propargylic carbonates at room temperature affording fully substituted allenes.It is confirmed that the excellent designed regioselectivity for the C-C triple bond insertion is induced by the coordination of the carbonyl group in the directing carbonate group as well as the steric effect of the tertiary O-linked carbon atom.When an optically active carbonate was used,surprisingly high efficiency of chirality transfer was realized,affording fully substituted allenes in excellent ees.Isoindolin-1-ones are very important species in natural or bio-active compounds and useful building blocks in organic synthesis.Based the results above and previous works on the cyclization reactions of allenes in our group,we have developed a rhodium-catalyzed green synthesis of these skeletons via a sequential C-H activation/allene formation/cyclization pathway by applying water as the solvent.The reaction was highly regioselective with tolerating different functional groups.After mechanistic studies,we believed that Rh was important for the cyclization step and AcOH helped the dissociation of Rh from the product by protonlysis.Part ?.We present a Rh(?)-catalyzed coupling between easily available arenes and propargylic alcohols at room temperature affording fully substituted allenes with H2O as the only by-product.When chiral propargylic alcohols were used,asymmetric C-H functionalization was realized with prefect chirality transfer,affording tetra-substituted allenes with excellent ees.Based on careful mechanistic studies,it is confirmed that the excellent reversed regioselectivity for the C-C triple bond insertion is induced by the steric effect of tertiary carbon center as well as the weak coordination nature of the hydroxyl oxygen with Rh,which is also responsible for the stereospecificity of the unique syn-?-OH elimination forming allenes with an excellent efficiency of chirality transfer.After KIE studies,it was found that the ?-OH elimination is rate determining.The synthetic potentials of the products have also been demonstrated.Part ?.We developed a Rh(?)-catalyzed cyclization reaction between easily available arenes and 1-alkynylic cyclobutanols affording isoquinolin-1(2H)-ones regioselectively with the combination of C-H activation and C-C bond activation.It is believed that the excellent regioselectivity of the C-C triples bond insertion is induced by weak coordination from hydroxyl oxygen.After detailed mechanistic studies,we found that afther C-C cleavage step,the formed Rh intermediate would "walk" on the carbon chain to a of the carbonyl group and finally protonlyzed by enol isomerization.