The first theoretical study on the mechanism of [RhCl(CO)2]2-catalyzed [5 + 1] cycloadditions of 3-acyloxy-1,4-enyne (ACE) and CO has been performed using density functional theory (DFT) calculations. The effect of ester on reactivity of this reaction has been investigated. The computational results have revealed that the preferred catalytic cycle involves the sequential steps of 1,2-acyloxy migration, CO insertion, reductive elimination to form ketene intermediate, 6π-electroncyclization, and aromatization to afford the resorcinol product. The 1,2-acyloxy migration is found to be the rate-determining step of the catalytic cycle. The electron-rich p-dimethylaminobenzoate substrate promotes 1,2-acyloxy migration and significantly increases the reactivity by stabilizing the positive charge building up in the oxocyclic transition state.

By switching the position of the alkene and alkyne, a new type of 3-acyloxy-1,4-enyne (ACE) five-carbon building block was developed for Rh-catalyzed intramolecular [5+2] cycloaddition. An electron-withdrawing acyl group on the alkyne termini of the ACE was essential for a regioselective 1,2-acyloxy migration. This new method provided bicyclic [5.3.0]decatrienes that are different from previous methods because of the positions of the alkenes and the acyloxy group. Multiple mechanistic pathways become possible for this new [5+2] cycloaddition and they are investigated by computational studies.

A novel cyclization of 3-acyloxy-1,5-enynes is developed in the presence of PtI2 for the synthesis of substituted unsymmetrical m-terphenyls in good to excellent yields. Two unique steps are involved in this transformation, which includes the elimination of HOAc and benzyl group migration. DFT calculations indicated that the rate-determining step is the migration of the benzylic carbocation to form a zwitterionic intermediate followed by the elimination of HOAc. The subsequent cyclopropanation of the zwitterionic intermediate is the regioselectivity-determining step.

The (5+2) cycloaddition reaction utilising cycloalkenes is rare, although it is one of the most efficient methods of constructing seven-membered fused rings because of its high atom- and step-economy. In this study, we used quantum mechanical calculations to predict the plausibility of using the Rh-catalysed intermolecular (5+2) cycloaddition of 3-acyloxy-1,4-enynes and cycloalkenes to produce fused seven-membered carbocycles. The calculation results suggest a convenient, highly efficient and energetically practical approach. Strained cycloalkenes, such as cyclopropene, have been predicted to be active, and the desired bicyclic product should be favoured, accompanied by the formation of byproducts from rearrangement reactions. The energy barriers of the alkene insertion step were analysed by the distortion/interaction model to disclose the origins of the different reactivities of cycloalkenes with different ring sizes.

PtI 2-Catalyzed Cyclization of 3-Acyloxy-1,5-enynes with the Elimination of HOAc and a Benzyl Shift: Synthesis of Unsymmetrical m-Terphenyls. -The utility of the method is exemplified by the preparation of a photoelectrically interesting multiphenyl compound [cf. (X)]. The regioselectivity of the reaction is examined by extensive evaluation of its mechanism via DFT-calculations. -(HUANG, K.; KE, X.; WANG, H.; WANG, J.; ZHOU, C.; XU*, X.; LIU, L.; LI, J.; Org. Biomol. Chem. 13 (2015) 15, 4486-4493, http://dx.