Reactions of Propargyl Compounds Containing a Cyclobutyl Group Induced by a Ruthenium Complex

Lithiated three-membered heterocycles as chiral nucleophiles in the enantioselective synthesis of 1-oxaspiro[2,3]hexanes

The reaction between configurably stable α-lithiated oxiranes and 3-substituted cyclobutanones allows obtaining enantiomerically enriched cyclobutanols (er > 98 : 2). These adducts, subjected to base-mediated Payne rearrangement, lead to the synthesis of a new class of oxaspirohexanes, useful precursors of 2,4-disubstituted cyclopentanones.

Cyclization Reactions of Aryl Propargyl Acetates with Tethered Epoxide Induced by Ruthenium Complex

Reactions of the ruthenium complex [Ru]Cl ([Ru]=Cp(PPh₃ )₂ Ru; Cp=η⁵ -C₅ H₅ ) with several aryl propargyl acetates, each with an ortho-substituted chain of various length containing an epoxide on the aromatic ring and with or without methyl substitutents on the epoxide ring, bring about novel cyclizations. The cyclization reactions of HC≡CCH(OAc)(C₆ H₄ )CH₂ (RC₂ H₂ O) (R=H, 6 a; R=CH₃ , 6 b, where RC₂ H₂ O is an epoxide ring) in MeOH give the vinylidene complexes 5 a-b, respectively, each with the Cβ integrated into a tetrahydro-5H-benzo[7]annulen-6-ol ring. A C-C bond formation takes place between the propargyl acetate and the less substituted carbon of the epoxide ring. Further cyclizations of 5 a-b induced by HBF₄ give the corresponding vinylidene complexes 8 a-b each with a new 8-oxabicyclo-[3.2.1]octane ring by removal of a methanol molecule in high yield. For similar aryl propargyl acetates with a shorter epoxide chain, the cyclization gives a mixture of a vinylidene complex with a tetrahydronaphthalen-1-ol ring and a carbene complex with a tricyclic indeno-furan ring. For the cyclization of 18, with a longer epoxide chain, opening of the epoxide is required to afford the vicinal bromohydrin 22, then tandem cyclization occurs in one pot. Products are characterized by spectroscopic methods as well as by XRD analysis.

Reactions of Ruthenium Complexes Containing Pentatetraenylidene Ligand

Two ruthenium acetylide complexes [Ru]-C≡C-C≡C-C(OR)(C₃ H₅ )₂ (2, R=H and 2 a, R=CH₃ ; [Ru]=Cp(PPh₃ )₂ Ru) each with two cyclopropyl rings were synthesized from TMS-C≡C-C≡C-C(OH)(C₃ H₅ )₂ (1; TMS=trimethylsilyl). Treatments of 2 and 2 a with allyl halide in the presence of KPF₆ afforded the vinylidene complexes 3 and 3 a, respectively. When NH₄ PF₆ was used, instead of KPF₆ , additional ring-opening reaction took place on one of the three-membered ring. Treatment of [Ru]Cl with 1,3-butadiyne (6), bearing an epoxide ring, afforded acetylide complex 7 with a furyl ring. Treatment of 2 a with Ph₃ CPF₆ presumably afforded pentatetraenylidene complex {[Ru]=C=C=C=C=C(C₃ H₅ )₂ }[PF₆ ] (10), which was not isolated. Additions of various alcohols in a solution of 10 generated a number of disubstituted allenylidene complexes {[Ru]=C=C=C(OR)-C=C(C₃ H₅ )₂ }[PF₆ ] (11). Treatment of 11 with K₂ CO₃ afforded the acetylide complex 12 bearing a carbonyl group, characterized by single X-ray diffraction analysis. Addition of a primary amine to 10 caused cleavage of the farthermost C=C bond and several allenylidene complexes {[Ru]=C=C=C(Me)(NHR)}[PF₆ ] (18) were isolated.