One-Step Synthesis of Heteroaromatic-Fused Pyrrolidines via Cyclopropane Ring-Opening Reaction: Application to the PKCβ Inhibitor JTT-010

Reactions of ruthenium-allenylidene complexes tethering a cyclopropyl group

Two cyclopropyl allenylidene complexes [Ru]=C=C=C(R)(C(3)H(5)) ([Ru]=[RuCp(PPh(3))(2)], Cp=Cyclopentadienyl; R=thiophene (2a) and R=Ph (2b)) are prepared from the reactions of [Ru]Cl with the corresponding 1-cyclopropyl-2-propyn-1-ol in the presence of KPF(6). Thermal treatment, halide-anion addition, and palladium-catalyzed reactions of 2a and 2b all lead to a ring expansion of the cyclopropyl group, giving the vinylidene complexes 4a and 4b, respectively, each with a five-membered ring. This ring expansion proceeds by C-C bond formation between Cβ of the cumulative double bond and a methylene group of the cyclopropyl ring. In the reaction of 2a with pyrrole, consecutive formation of two C-C bonds, one between C-2 of pyrrole and Cγ of 2a and the other between C-3 of pyrrole and Cα, results in the formation of 6a. The reaction proceeds by addition of pyrrole and 1,3-proton shifts. The hydrogenation of 2a by NaBH(4) is carried out in different solvents. The cumulative double bonds are reduced regioselectively to give a mixture of 7a and 8a. Interestingly, use of different solvents leads to different ratios of 7a and 8a. Presence of a protic solvent like methanol in dichloromethane or chloroform solution increases the yield of 8a, thus revealing that both the rates of hydroboration and deboronation increase. The structures of two new complexes 4a and 6a have been firmly established by X-ray diffraction analysis.

Directed oxidative cyclizations to C2- or C4-positions of indole: efficient construction of the bicyclo[4.3.1]decane core of welwitindolinones

Regiocontrolled oxidative cyclizations of 3-substituted indoles are described herein. Specifically, it is shown that the installation of a chloride at C2 alters the inherent propensity for cyclization at the 2-position of indole so as to favor the 4-position, enabling the construction of the unique framework found in most welwitindolinone alkaloids. The chloride functions here as more than a blocking group, as it also provides ready access to the corresponding oxindole.

N-heterocyclic carbene-catalyzed domino ring-opening/redox amidation/cyclization reactions of formylcyclopropane 1,1-diesters: direct construction of a 6-5-6 tricyclic hydropyrido[1,2-a]indole skeleton

Catalyzed by N-heterocyclic carbenes (NHCs), domino ring-opening/redox amidation/cyclization reactions of the readily available formylcyclopropane 1,1-diesters with 2-chloro-1H-indole-3-carboaldehydes were reported. This methodology provides an efficient and direct construction of a 6-5-6 tricyclic hydropyrido[1,2-a]indole skeleton, which can be potentially applied for the synthesis of several types of polycyclic indole alkaloids.