The N−H and C−H bond activation reactions at ambient conditions of seven different secondary allyl amines (Aa−g) with bis(η 5 :η 1 -pentafulvene)titanium complexes (1) h a v e b e e n i n v e s t i g a t e d . B i s ( η 5 : η 1adamantylidenepentafulvene)titanium (1a) reacts with Nallylaniline (Aa), N-allylbenzylamine (Ac), N-allyl-tert-butylamine (Ad), N-allylcyclohexylamine (Ae), and N-allyl-2methylaniline (Af) to give the 1-azabutadiene complexes 2a,c−f with high yields. They are the first complexes of the CH 2 -terminated monoazadiene RNCHCHCH 2 . Using bis(η 5 :η 1 -di-p-tolylpentafulvene)titanium (1b), which exhibits a less Brønsted basic C exo center, and Aa, the β-C−H bond activation can be slowed down so much that the agostic interaction between the titanium center and the C−H bond is detectable via NMR measurements at room temperature. In the reactions of the titanium azabutadiene complexes 2a,b and 3a with carbon monoxide a ligand exchange is observed, forming the titanocene dicarbonyls 4a,b.
Robinson-type cyclopentannulations of cyclic β-oxoesters possessing a 1,4-diketone moiety are accomplished under four different Brønsted basic reaction conditions. Using pyrrolidine/acetic acid in DMSO, an oxohexahydrocyclopenta[a]indene (42%) and an N-Boc-protected oxohexahydrocyclopenta[c]pyridine derivative (62%) are obtained with retention of the ester moieties. The latter compound defines an interesting new scaffold for medicinal chemistry with three positions allowing further derivatizations. The use of KOtBu in DMSO or NaH in toluene leads to cyclopentene derivatives with either partial ester saponification and decarboxylation or displacement of the ester moiety within the carbon skeleton. With aqueous KOH, the cyclopentannulations are successful in almost all cases, but with the ester moieties cleaved off. The respective bicyclic and tricyclic products are obtained in good to excellent yields. The 1,4-diketone starting materials are prepared by cerium-catalyzed oxidative coupling of β-oxoesters with isopropenyl acetate. Alternatively, a two-step sequence consisting of α-propargylation followed by palladium-catalyzed alkyne hydration is used.
The ring enlargement reactions at ambient temperatures of non C-terminus substituted monoazabutadiene (η -RN=CHCH=CH ) titanium complexes 2 are investigated. The insertion of aldehydes/ketones (five examples) and nitriles (four examples) into the Ti-C bonds result in expansion of the five-membered rings to uncommon seven-membered titanacycles 3 and 4 in good yields. These new compounds are fully characterized by NMR spectroscopy and single-crystal X-ray diffraction. In subsequent reactions, the seven-membered ring systems are protolyzed and the released organic fragments are isolated. Whereas the aldehyde/ketone insertion products 3 form substituted δ-amino alcohols 5 after reduction with NaBH CN, the nitrile insertion products 4 form substituted pyrroles 6 via cyclization.
Driven by the shortage of known effective possibilities for the synthesis of 4-hydroxy-3,4-dihydro-2H-1,3-thiazine-2-thiones on the one hand and the promising potential of these structures as novel drug candidates on the other hand, synthetic access to 4-hydroxy-3,4-dihydro-2H-1,3-thiazine-2-thiones was developed. The desired products could be synthesized effectively and facilely starting from β-chlorovinyl aldehydes with the aid of a new MCR (multicomponent reaction). Furthermore, the 4-hydroxy-3,4-dihydro-2H-1,3-thiazine-2-thiones are shown to be appropriate substrates in the preparation of diverse annulated polycyclic systems.
Sulfonic acids serve as interesting, yet not intensively studied alternatives to carboxylic acids as linker units in coordination polymers. In this study, we present the synthesis of hybrid sulfonic acids with pyridine and pyrimidine units as additional nitrogen donor moieties. Four biaryl compounds consisting of a 4‐mono‐ or 3,5‐disulfophenyl ring and a 4‐pyridyl or 5‐pyrimidyl residue were prepared by Suzuki coupling reaction. In these cases, tert‐butylthio groups were utilized as precursor functions for the sulfonic acid residues. The tert‐butyl residues were cleaved with BBr3, the intermediate thiols trapped with acetyl chloride and then oxidized with H2O2. Furthermore, two pyrimidine derivatives with 5‐ethynyl linkers and 4‐mono‐ and 3,5‐disulfophenyl moieties were prepared by Sonogashira coupling. In these cases, the sulfonic acids were applied as neopentyl esters. Finally, the neopentyl groups were simply cleaved by thermolysis.
Cyclic α‐(ortho‐iodophenyl)‐β‐oxoesters were converted in a ring‐expanding transformation to furnish benzannulated cycloalkanone carboxylic esters. The reaction sequence started by electrochemical reduction of the iodoarene moiety. In a mechanistic rationale, the resulting carbanionic species was adding to the carbonyl group under formation of a strained, tricyclic benzocyclobutene intermediate, which underwent carbon–carbon bond cleavage and rearrangement of the carbon skeleton by retro‐aldol reaction. The scope of the reaction sequence was investigated by converting cyclic oxoesters with different ring sizes yielding benzocycloheptanone, ‐nonanone and ‐decanone derivatives in moderate to good yields. Furthermore, acyclic starting materials and cyclic compounds carrying additional substituents on the iodophenyl ring were submitted to this reaction sequence. The starting materials for this transformation are straightforwardly obtained by conversion of β‐oxoesters with phenyliodobis(trifluoroacetate).
Sulfonic acids serve as interesting, yet not intensively studied alternatives to carboxylic acids as linker units in coordination polymers. In this study, we present the synthesis of hybrid sulfonic acids with polar, rigid biphenyl moieties and disordered highly fluorinated alkyl chains. Consequently, eight biphenyl sulfonic and disulfonic acids with one or two perfluoroalkyl chains were prepared. The key steps within the synthesis include two palladium catalyzed C–C bond formations: The perfluoroalkyl residue is installed by Heck reaction (up to 91 %) using 1H,1H,2H‐perfluorinated alkenes (C6 and C8) and the biphenyl unit is established by a Suzuki coupling (up to 88 %) of boronic acids bearing one or two protected thiol groups. Finally, these thiol groups are converted into the sulfonic acids by N‐chlorosuccinimide mediated oxidation followed by hydrolysis of the respective sulfonyl chloride.
With its two carboxylate functions arranged in an 90°a ngle, 1,3-allenedicarboxylic acid (point group C 1 ) possesses a symmetry distinguished from all other dicarboxylic acids which are generally utilized as linker compounds in coordination polymers or MOFs. Crystal structures of coordination compounds with the 1,3-allenedicarboxylate dianion are reported herein for the first time. The diacid was converted with metal carbonates M 2 CO 3 to furnish the crystalline lithium, sodium, rubidium, cesium and thallium(I) compounds. In the solid state, their [a]
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