The stabilisation of 3,4-pyridyne (1) by an alkoxy group adjacent to the ring nitrogen is reported. The regioselective lithiation of 2-ethoxy- (14), 2-methoxy- (18), 2-isopropoxy- (19) and 6-isopropoxy- (26) -3-chloropyridines with tert-butyllithium at low temperatures, followed by elimination of lithium chloride affords 2- and 6-alkoxy-3,4-pyridynes. These species are trapped in situ with furan in a Diels–Alder reaction to give 5–8 in 66–89% yield, and do not give products typical of polymerisation or nucleophilic addition to the 3,4-pyridyne intermediates. As a comparison treatment of 3-chloropyridine with furan and LDA gives only 19% of adduct (4). We also report the novel use of the isopropoxy (rather than methoxy) group in these systems, which can act as a heteroatomic electron donating group which inhibits α-lithiation by tert-butyllithium because of its increased steric bulk.
protocol for the synthesis of 1-heteroaryl-4-(N-methyl)aminopiperidines starting from heteroaryl chloride derivatives is described. A broad range of 1-heteroaryl-4-(N-Boc-N-methyl)aminopiperidine derivatives were obtained in good to excellent yields using DavePhos as optimal ligand for Pd-catalyzed Buchwald-Hartwigamination reaction. After a mild and efficient acidolysis the amination products could
A regioselective 3,4-difunctionalization of pyridines was performed. Lithiation and transmetalation with arylmagnesiums gave 3,4-pyridyne intermediates. Addition of magnesium species led to 3-pyridylmagnesiums which were quenched with electrophiles.
Rh(I)-Catalyzed Ring-Opening of Hetaryne−Furan Diels−Alder Adducts: Rapid Access to Stereochemically Defined Heterocyclic Scaffolds
作者:Trung D. Nguyen、Robert Webster、Mark Lautens
DOI:10.1021/ol200057j
日期:2011.3.18
Probing the nucleophilic ring-opening of various bicyclic [2.2.1] hetaryne-furan Diels-Alder adducts revealed that efficient reactivity could be observed with heteroatom nucleophiles by using a cationic Rh(I) complex in combination with a chiral Josiphos-type phosphine ligand. Remarkably, this catalyst system was not impeeded by the incorporation of a heteroatom into the substrate. Racemic materials afforded separable mixtures of enantioenriched regioisomers, indicating that strong reagent control is operative.
6,7-DIHYDROPYRAZOLO[1,5-A]PYRAZIN-4(5H)-ONE COMPOUNDS AND THEIR USE AS NEGATIVE ALLOSTERIC MODULATORS OF MGLUR2 RECEPTORS