Pd-Catalyzed Ring Opening of Oxa- and Azabicyclic Alkenes with Aryl and Vinyl Halides: Efficient Entry to 2-Substituted 1,2-Dihydro-1-naphthols and 2-Substituted 1-Naphthols

An efficient syntheses of 2-substituted 1,2-dihydro-1-naphthols and 2-substituted 1-naphthols has been developed that involves the sequential palladium-catalyzed ring opening of oxabicyclic alkenes with aryl and vinyl halides followed by oxidation of with IBX. In the first step of the sequence, a combination of Pd(OAc)2, PPh3, Zn, and PMP in dry DMF was employed to catalyze the ring opening of 7-oxabenzonorbornadienes with aryl and vinyl halides to afford the corresponding cis-2-substituted 1,2-dihydronaphthols in good to excellent yields. These reactions occurred under very mild conditions with a variety of aryl halides bearing electron-withdrawing or -donating groups. Similarly, a 7-azabenzonorbornadiene substituted with an electron-withdrawing group on the nitrogen atom underwent facile ring-opening reaction with aryl halides to provide cis-2-substitued (1,2-dihydro-1-naphthyl)carbamates in excellent yields. Oxidation of the intermediate1,2-dihydro-1-naphthols using IBX yielded the corresponding 2-substituted 1-naphthols in good to excellent yields

Facile Synthesis of 2-Substituted 1,2-Dihydro-1-naphthols and 2-Substituted 1-Naphthols

The palladium-catalyzed ring opening of dimethoxy oxabenzonorbornadiene with aryl or vinyl halides occurred under very mild conditions to give substituted 1,2-dihydronaphthols that were oxidized with IBX to furnish substituted naphthols in excellent overall yields

Attempts To Improve the Overall Stereoselectivity of the Ireland−Claisen Rearrangement

With focus on the steric effects present in the transition states for the [3,3]-sigmatropic rearrangement, the substrate 5 has been designed to improve the overall stereoselectivity of the Ireland−Claisen rearrangement. Experimentally, it has been found that (1) only Z-6 rearranges to 7 at 80 °C and (2) E-6 isomerizes to Z-6 at 80 °C, thereby allowing the transformation of 5 into 7 in an almost quantitative yield. To illustrate the usefulness of this approach, two additional examples are given

<i>C</i>-Aryl Glycosides via Tandem Intramolecular Benzyne−Furan Cycloadditions. Total Synthesis of Vineomycinone B₂ Methyl Ester

A triply convergent total synthesis of vineomycinone B2 methyl ester has been achieved by an approach with a longest linear sequence of 16 steps. The synthesis features the use of silicon tethers as disposable linkers to control the regiochemistry in two tandem Diels−Alder reactions of substituted benzynes and glycosyl furans to provide rapid access to the fully intact anthrarufin core of vineomycinone B2 methyl ester

Well-Controlled Block Polymerization/Copolymerization of Alkenes and/or Carbon Monoxide by Cationic Palladium Methyl Complexes

Cationic palladium imine−phosphine complexes [Pd(P−N)(CH3)(CH3CN)]+ catalyze the living block polymerization and copolymerization of olefins and/or carbon monoxide. The palladium-capped polymers, intermediates of the polymerization, were isolated

Initiation Steps for the Polymerization of Vinyl Ethers Promoted by Cationic Palladium Aqua Complexes

Both deuterium-labeled experimental and NMR spectroscopic analyses of poly(vinyl ether) offer the mechanistic insight into the polymerization, indicating that the cationic palladium aqua imine−phosphine complexes [(P∼N)PdMe(H2O)]BF4 (P∼N = o-C6H4(PPh2)(NCHAr)) promote the reaction via proton-transfer initiation. Insertion of vinyl ether into the Pd−Me bond in [(P∼N)PdMe(H2O)]BF4 does not proceed, but the single insertion of the same substrate into the Pd−acetal bond of [(P∼N)PdCOCH3(L)]BF4 provides the stable inserted product [(P∼N)PdCH(OEt)CH2COCH3]BF4, which has been characterized by an X-ray structural determination. However, these palladium complexes do not catalyze the polymerization or copolymerization of vinyl ether and carbon monoxide

Initiation Steps for the Polymerization of Vinyl Ethers Promoted by Cationic Palladium Aqua Complexes

Both deuterium-labeled experimental and NMR spectroscopic analyses of poly(vinyl ether) offer the mechanistic insight into the polymerization, indicating that the cationic palladium aqua imine−phosphine complexes [(P∼N)PdMe(H2O)]BF4 (P∼N = o-C6H4(PPh2)(NCHAr)) promote the reaction via proton-transfer initiation. Insertion of vinyl ether into the Pd−Me bond in [(P∼N)PdMe(H2O)]BF4 does not proceed, but the single insertion of the same substrate into the Pd−acetal bond of [(P∼N)PdCOCH3(L)]BF4 provides the stable inserted product [(P∼N)PdCH(OEt)CH2COCH3]BF4, which has been characterized by an X-ray structural determination. However, these palladium complexes do not catalyze the polymerization or copolymerization of vinyl ether and carbon monoxide

New Imine−Phosphine Palladium Complexes Catalyze Copolymerization of CO−Ethylene and CO−Norbornylene and Provide Well-Characterized Stepwise Insertion Intermediates of Various Unsaturated Substrates

New imine−phosphine palladium complexes [Pd(P−N)(CH3)(CH3CN)](BF4) (P−N = o-(diphenylphosphino)-N-benzaldimine derivatives) are synthesized and are found to be active for copolymerization of CO−ethylene and CO−norbornylene, respectively. Stepwise addition of carbon monoxide and various olefins into the new complexes is investigated

Conversion of Diamino-Substituted Carbene Complexes into the Isocyanide by Acylation

Treatment of cyclic diaminocarbene (M = Cr, Mo, W; m = 2, 3) with acylating agents resulted in the formation of the corresponding isocyanide complexes (CO)5MCN(CH2)mNH2-n(COR)n (M = Cr, Mo, W; m = 2, 3; n = 1, 2; R = Ph CH3) in high yields. It appears that the N-acyl group destabilizes the diaminocarbene complexes and causes the cleavage of the C−N bond to form the isocyanide product. The reaction pathway leading to the isocyanide complexes is discussed. The crystal structure of (CO)5WC⋮ N(CH2)2N(COPh)2 has been determined

Heterocyclyl Tetracyclines. 1. 7‑Trifluoromethyl-8-Pyrrolidinyltetracyclines: Potent, Broad Spectrum Antibacterial Agents with Enhanced Activity against Pseudomonas aeruginosa

Utilizing a total synthesis approach, the first 8-heterocyclyltetracyclines were designed, synthesized, and evaluated against panels of tetracycline- and multidrug-resistant Gram-positive and Gram-negative pathogens. Several compounds with balanced, highly potent in vitro activity against a broad range of bacterial isolates were identified through structure–activity relationships (SAR) studies. One compound demonstrated the best antibacterial activity against Pseudomonas aeruginosa both in vitro and in vivo for tetracyclines reported to date