Tandem cross-metathesis/hydrogenation: application to an enantioselective synthesis of pentadecyl 6-hydroxydodecanoate

The synthesis of pentadecyl 6-hydroxydodecanoate, a component isolated from the leaves of Artabotrys odoratissimus, has been achieved through a tandem cross-metathesis/hydrogenation sequence. The enantioselective synthesis required first the preparation of a homoallylic alcohol obtained by a free-metal allyl transfer from a camphor derivative to heptanal.     

A transition metal-free tandem process to pyrrolopyrazino[2,3-d]pyridazine-diones

A transition metal-free tandem process for the synthesis of pyrrolopyrazino[2,3-d]pyridazine-diones is described. The process is an efficient construction of this tricyclic system by a one-pot coupling/Smiles rearrangement/cyclization approach. This methodology has potential applications in the synthesis of biologically and medicinally relevant compounds.     

A convenient stereoselective synthesis of β-lactams from β-hydroxy-α-thioalkylesters prepared from Michael/aldol tandem reaction or stereoselective addition of thiols to the Baylis-Hillman adducts

A convenient stereoselective synthesis of β-lactams from thio-Michael/aldol tandem adduct is described. syn-Selective tandem reaction followed by amidation and intramolecular S_N2 reaction provided β-lactams in diastereomerically pure form. The tandem reaction with aliphatic aldehydes, on the other hand, afforded a mixture of diastereomers of corresponding tandem adducts in about 3:1 ratio so that the conversion to β-lactams afforded a diastereomeric mixture. As an alternative approach to prepare the tandem adducts, the stereoselective Michael addition of aliphatic thiols to Baylis-Hillman adduct was developed. The stereoselectivity was sensitive to the protective group at the hydroxyl group and TBS protection brought the most successful syn-selective formation of the tandem adducts. The procedure could be applied to the ketone derivatives of the Baylis-Hillman adduct but no selectivity was observed for the nitrile-Baylis-Hillman adducts. A similar conversion of the adduct provided desired β-lactams stereoselectively.     

Facile synthesis of isoquinolines by imination and subsequent palladacycle-catalyzed iminoannulation of internal alkynes

An efficient and facile synthesis of isoquinolines has been described via a tandem reaction of imination of o-halobenzaldehydes with tert-butyl amine and subsequent palladacycle-catalyzed iminoannulation of internal alkynes. This tandem reaction could be carried out successively in one pot without any special operation, and the annulation step could afford isoquinolines derivatives in moderate to good yields with high regioselectivity. In addition, the simple synthesis of indoles was realized by palladacycle-catalyzed annulation of o-iodoaniline or o-bromoanilines with internal alkynes.     

Synthetic evolutions in the nucleophilic addition to alkynes

This short account describes our efforts to transform the simple nucleophilic addition of alkynes into a more efficient, selective and environmentally benign synthetic tool. We have circumvented the lack of regioselectivity in the gold-catalyzed triple bond addition of water through neighboring group participation and in the process we developed a ‘functionalized hydration’ (multiple bond formation and hydration in a one-pot process) using fluorine-engendered cationic gold catalysis. In addition, we have conducted the synthesis of O-heterocycles through a gold-catalyzed tandem addition/cycloisomerization sequence, the synthesis of N-heterocycles through a copper-catalyzed cyclization-triggered addition of alkynes, and a green synthesis of thioethers ‘on water’ without catalyst or initiator. These nucleophilic synthetic evolutions, catapulted by a simple addition to an alkyne, will surely contribute to provide a wider synthetic access to sophisticated biological targets.     

A novel tandem process leading to functionalized glutarimides

The synthesis of various functionalized or spirobicyclic glutarimides by a novel tandem process has been disclosed. The reaction involves a base-catalyzed Michael addition of active methylene compounds to secondary conjugated amides, followed by intramolecular N-acylation of the carboxamido group. It provides a relatively general and simple access to useful synthetic intermediaries and potentially active pharmacological compounds. In addition, a novel group of spirobicyclic systems has been synthesized.     

Studies on the synthesis of the lasubine alkaloids

Formal syntheses of lasubine II and subcosine II have been completed by the synthesis of epi-lasubine II. The synthesis involves diastereoselective allylation of a methoxy isoxazolidine and a tandem hydrogenation process leading stereoselectively to a trisubstituted piperidine.     

Copper-catalyzed C–N coupling/C–H functionalization: A tandem approach to azole-fused quinazoline derivatives

A Cu-catalyzed tandem synthesis of azole-fused pyrimido[1,2-c]quinazolines and imidazo[1,2-c]quinazolines has been developed. The reaction is based on a C–N cross-coupling/C–H functionalization reaction of 2-(2-bromophenyl)-1,4,5,6-tetrahydropyrimidines with azoles. A variety of the desired polycyclic products were obtained in moderate to excellent yields.     

An efficient approach to isoquinoline via AgNO3-promoted 6-endo-dig cyclization followed by oxidative elimination of o-alkynylarylaldimines and its application in fluoride recognition

A novel 6-endo-dig cyclization followed by oxidation/elimination of o-alkynylarylaldimines with 4-hydroxybenzylamine was developed for preparation of isoquinolines. The intermediates of this tandem reaction were monitored by mass spectroscopy (MS) to confirm the reaction pathway. This methodology was further applied to the design and synthesis of a novel ratiometric chemosensor for determination of fluoride.     

Total synthesis of calystegine A7

A straightforward chiral pool synthesis for the glycosidase inhibitor calystegine A₇ (isolated from Lycium chinense) from methyl α-d-glucopyranoside is described. Keysteps of this synthesis include a ultrasound assisted Zn-mediated tandem ring opening reaction followed by a Grubbs' catalyst mediated ring closure metathesis.     

Triflic anhydride-mediated tandem formylation/cyclization of cyanoacetanilides: a concise synthesis of glycocitlone alkaloids

A method is presented for the concise synthesis of 3-formyl-4-hydroxyquinolin-2(1H)-ones through triflic anhydride-mediated tandem formylation/cyclization of cyanoacetanilides. This tandem process was successfully used for the rapid syntheses of glycocitlones A and C.     

Facile entry to polycyclic indolylhydroquinoline skeletons via tandem C-alkylation and intramolecular S-alkylation

An efficient, single step synthesis of hitherto unknown indole-annulated pentacyclic indolylhydroquinolines via tandem C-alkylation and intramolecular S-alkylation of indolin-2-thiones with N-alkylquinolinium salts in excellent yields (83-95%) is reported. This facile approach provides a powerful entry into polycyclic structures containing nitrogen and sulfur related to alkaloids. The structure of the product was determined by Röntgen crystal structure analysis.     

An efficient approach for monosulfide bridge formation in solid-phase peptide synthesis

An efficient approach for the synthesis of cyclic peptides containing unnatural thioether side-chain bridges, based on the use of (2S)-9-fluorenylmethyl-2-[(tert-butoxycarbonyl)amino]-4-iodobutanoate and its homologue 5-iodopentanoate, derived from Boc-l-Asp-OFm and Boc-l-Glu-OFm, respectively, is reported. The synthesis was performed by a tandem combination of solid-phase peptide synthesis and microwave-assisted cyclization strategy.     

Diastereospecific synthesis of novel [3.6.6.4.7]-fused pentacyclic β-lactams by 6-exo-trig, 7-endo-dig tandem radical cyclization

An efficient synthesis of pentacyclic β-lactams has been achieved in high yield via a novel 6-exo-trig, 7-endo-dig tandem radical cyclization.     

One-pot approach to 2-arylbenzoxazinone derivatives from 2-alkynylanilines using copper-mediated tandem reactions

In this study, we describe a one-pot method to obtain a variety of 2-arylbenzoxazinones and N-benzoyl anthranilic acid by using a copper catalyst and molecular oxygen as oxidants. This protocol involves tandem cyclization and oxidative processes of 2-alkynylanilines to afford significant motifs in synthetic and medicinal chemistry with moderate yields. We also demonstrated that combining the Sonogashira coupling and the developed method realized the synthesis of 2-arylbenzoxazinones derivatives from commercially available 2-iodoanilines and terminal acetylenes.     

One-pot two-step tandem reactions for selective synthesis of pyrrolo[2,1-a]isoquinolines and dihydro-, tetrahydro-derivatives

A sequential one-pot two-step tandem reaction for selective and efficient synthesis of pyrrolo[2,1-a]isoquinoline and its dihydro- and tetrahydro-derivatives has been developed. The tandem reactions of isoquinoline, α-halogenated methylene compounds, aromatic aldehydes, and cyanoacetamide firstly give tetrahydropyrrolo[2,1-a]isoquinolines as main products. The corresponding pyrrolo[2,1-a]isoquinolines and dihydropyrrolo[2,1-a]isoquinolines can be obtained directly by controlling oxidation with DDQ. The mechanism of this tandem reaction involved the 1,3-dipolar cycloaddition of isoquinolinium ylide as the key step. A unique elimination of the amido group preferring to the cyano group has been observed.     

Formal total synthesis of aspergillides A and B

The formal total synthesis of the cytotoxic 14-membered macrolides, aspergillides A and B is described. A combination of a chiron approach and an asymmetric synthesis is adopted for the synthesis of the target macrolides. The required 2,6-syn and 2,6-anti tetrahydropyrans were constructed via a tandem Sharpless asymmetric epoxidation and 6-exo cyclization on δ-hydroxy allylic alcohols, as the key steps. The requisite chiral synthon was prepared from l-ascorbic acid.     

New synthesis of benzo[b]furan and indole derivatives from 1,1-dibromo-1-alkenes using a tandem Pd-assisted cyclization-coupling reaction

We report a new flexible method for the synthesis of 2-functionalized benzo[b]furans and indoles from readily available o-(2,2-dibromovinyl)-phenol, -aniline or -acetanilide using a tandem Pd-assisted cyclization-coupling reaction.     

I2-promoted tandem cyclization to synthesize polysubstituted pyrano[3,2-c]chromene-2,5-diones

An efficient and convenient method for the synthesis of various substituted pyrano[3,2-c]chromene-2,5-diones was developed via the I₂-promoted tandem cyclization of commercially available aryl methyl ketones and 4-hydroxycoumarins. Preliminary mechanism studies indicated that the reaction involved a consecutive iodination/Kornblum oxidation/annulation process. HI produced in the I₂-DMSO system acted as an important promoter, accelerating the annulation protocol.     

Photoredox-catalyzed sulfenylation/cyclization of N-aryl-N-tosylpropargylamine with disulfide: A concise route to 3-phenylthioquinoline

A facile and novel protocol for one-pot synthesis of 3-phenylthioquinoline derivates via visible-light induced tandem cyclization of N-aryl-N-tosylpropargylamine with disulfides was developed. This unprecedented method, involving CS bond formation, detosylation and aromatization, afforded the desired products in a broad substrate scope under mild conditions.