The study focuses on the synthesis, characterization, and reactivity of rhodium(III) complexes with N-boranyl-1,3,5-triaza-7-phosphaadamantane (N–B–PTA(BH3)) ligands. The reaction of N–B–PTA(BH3) with [CpRhCl(l-Cl)]2 yields complexes [CpRh{N–B–PTA(BH3)}Cl2] (3) or [CpRh{N–B–PTA(BH3)}2Cl]Cl (5), containing one or two P-bonded boronated PTA ligands. The hydride [CpRh{N–B–PTA(BH3)}H2] (8) was also obtained by reaction with NaBH4. These complexes can undergo hydrolysis to produce dihydrogen and H3BO3, along with PTA derivatives. Furthermore, the reaction of complex 8 with electron-poor alkynes results in the formation of alkene complexes [Cp*Rh{N–B–PTA(BH3)}(g2-CH2 = CHR)] without affecting the N–BH3 moiety. The X-ray crystal structures of complexes 3 and 10 were determined and discussed, providing insights into the coordination chemistry and potential applications of these water-soluble rhodium complexes.
The study focuses on the synthesis of substituted 2-azabicyclo[3.2.1]octadienes, which are significant in the creation of natural products and biologically active compounds, through the ring expansion of substituted norbornadienes using toluenesulfonyl azide. The researchers explored the regioselectivity of the cycloaddition/rearrangement process with various mono- and disubstituted norbornadienes, finding that both types could be converted into the bicyclooctadiene ring system with high regiocontrol and in moderate to excellent yields. The study also investigated the impact of different substituent groups on the reaction's outcome, noting that electron-withdrawing groups resulted in little to no product, while hydroxymethyl derivatives provided a moderate yield of a single regioisomer. The synthesized 2-azabicyclo[3.2.1]octadienes can be further modified to yield highly substituted derivatives of the 2-azabicyclo[3.2.1]octane ring system, which is prevalent in natural products and pharmacologically active molecules, thus providing a valuable route for the synthesis of these complex structures.
The study presents the second total synthesis of Brevisamide, a marine cyclic ether alkaloid derived from Karenia brevis. The streamlined synthesis was achieved in 21 steps with a 5.2% overall yield, featuring a key SmI2 reductive cyclization step to access the tetrasubstituted pyran core. Key chemicals used in the study include monobenzyl protected-1,4-butane diol, which served as the starting material for the synthesis of pyran 3; ethyl propiolate, used in the 1,4-addition to form intermediate 9; and phosphonate ester 2, synthesized through a series of reactions including a Wittig reaction and an Arbuzov reaction, which was crucial for the Horner-Wadsworth-Emmons reaction to assemble the western C1-C4 and eastern C5-C15 fragments. The purpose of these chemicals was to construct the complex structure of Brevisamide through a series of strategic synthetic steps, ultimately leading to the successful synthesis of the natural product.
