N-Phthalimide as a Site-Protecting and Stereodirecting Group in Rhodium-Catalyzed C-H Functionalization with Donor/Acceptor Carbenes

The rhodium-catalyzed enantioselective C-H functionalization of unactivated C-H bonds by means of donor/acceptor carbene-induced C-H insertion was extended to substrates containing nitrogen functionality. The rhodium-stabilized donor/acceptor carbenes were generated by rhodium-catalyzed decomposition of aryldiazoacetates. The phthalimido group was the optimum nitrogen protecting group. C-H functionalization at the most sterically accessible methylene site was achieved using Rh₂(S-2-Cl-5-BrTPCP)₄ as catalyst, whereas Rh₂(S-TPPTTL)₄ was the most effective catalyst for C-H functionalization at tertiary C-H bonds and for the desymmetrization of N-phthalimidocyclohexane.

Dirhodium C-H Functionalization of Hole-Transport Materials

Hole-transport materials (HTMs) based on triarylamine derivatives play important roles in organic electronics applications including organic light-emitting diodes and perovskite solar cells. For some applications, triarylamine derivatives bearing appropriate binding groups have been used to functionalize surfaces, while others have been incorporated as side chains into polymers to manipulate the processibility of HTMs for device applications. However, only a few approaches have been used to incorporate a single surface-binding group or polymerizable group into triarylamine materials. Here, we report that Rh-carbenoid chemistry can be used to insert carboxylic esters and norbornene functional groups into sp² C-H bonds of a simple triarylamine and a 4,4'-bis(diarylamino)biphenyl, respectively. The norbenene-functionalized monomer was polymerized by ring-opening metathesis; the electrochemical, optical, and charge-transport properties of these materials were similar to those of related materials synthesized by conventional means. This method potentially offers straightforward access to a diverse range of HTMs with different functional groups.

Catalyst Controlled Site- and Stereoselective Rhodium(II) Carbene C(sp3)-H Functionalization of Allyl Boronates

Rhodium(II) catalyst-controlled site- and stereoselective carbene insertion into the distal allylic C(sp³)-H bond of allyl boronates is reported. The optimum chiral catalyst for this reaction is Rh₂(S-TPPTTL)₄. The fidelity and asymmetric induction of this catalytic transformation allows for a highly diastereoselective and enantioselective C-C bond formation without interference from the allyl boronate functionality. The resulting functionalized allyl boronates are susceptible to stereoselective allylations, generating products with control of stereochemistry at four contiguous stereogenic centers.

Design, Synthesis, and Evaluation of Extended C4-Symmetric Dirhodium Tetracarboxylate Catalysts

The synthesis and evaluation of six C4-symmetric bowl-shaped dirhodium tetracarboxylate catalysts are described. These elaborate high symmetry catalysts are readily generated by means of the self-assembly of four C1-symmetric ligands around the dirhodium core. These catalysts are capable of highly site-selective, diastereoselective and enantioselective C-H functionalization reactions by means of donor/acceptor carbene-induced C-H insertions.

Leveraging Regio- and Stereoselective C(sp3)-H Functionalization of Silyl Ethers to Train a Logistic Regression Classification Model for Predicting Site-Selectivity Bias

The C-H functionalization of silyl ethers via carbene-induced C-H insertion represents an efficient synthetic disconnection strategy. In this work, site- and stereoselective C(sp³)-H functionalization at α, γ, δ, and even more distal positions to the siloxy group has been achieved using donor/acceptor carbene intermediates. By exploiting the predilections of Rh₂(R-TCPTAD)₄ and Rh₂(S-2-Cl-5-BrTPCP)₄ catalysts to target either more electronically activated or more spatially accessible C-H sites, respectively, divergent desired products can be formed with good diastereocontrol and enantiocontrol. Notably, the reaction can also be extended to enable desymmetrization of meso silyl ethers. Leveraging the broad substrate scope examined in this study, we have trained a machine learning classification model using logistic regression to predict the major C-H functionalization site based on intrinsic substrate reactivity and catalyst propensity for overriding it. This model enables prediction of the major product when applying these C-H functionalization methods to a new substrate of interest. Applying this model broadly, we have demonstrated its utility for guiding late-stage functionalization in complex settings and developed an intuitive visualization tool to assist synthetic chemists in such endeavors.

Distal Allylic/Benzylic C-H Functionalization of Silyl Ethers Using Donor/Acceptor Rhodium(II) Carbenes

Regio- and stereoselective distal allylic/benzylic C-H functionalization of allyl and benzyl silyl ethers was achieved using rhodium(II) carbenes derived from N-sulfonyltriazoles and aryldiazoacetates as carbene precursors. The bulky rhodium carbenes led to highly site-selective functionalization of less activated allylic and benzylic C-H bonds even in the presence of electronically preferred C-H bonds located α to oxygen. The dirhodium catalyst Rh2 (S-NTTL)4 is the most effective chiral catalyst for triazole-derived carbene transformations, whereas Rh2 (S-TPPTTL)4 works best for carbenes derived from aryldiazoacetates. The reactions afford a variety of δ-functionalized allyl silyl ethers with high diastereo- and enantioselectivity. The utility of the present method was demonstrated by its application to the synthesis of a 3,4-disubstituted l-proline scaffold.