An expeditious synthesis of hexahydrobenzo[f]isochromenes and of hexahydrobenzo[f]isoquinoline via iodine-catalyzed Prins and aza-Prins cyclization

Homoallylic alcohols (primary, secondary, or tertiary containing an endocyclic or an exocyclic double bond) react with equimolar amounts of aldehydes (aliphatic or aromatic) and ketones (aliphatic) in the presence of 5 mol % of iodine. This Prins cyclization was used in the preparation of hexahydrobenzo[f]isochromenes and of a 4-hydroxy-tetrahydropyran, in 54-81% yield. The procedure is also efficient for an aza-Prins cyclization of a homoallylic sulfonamide and benzaldehyde, producing a hexahydrobenzo[f]isoquinoline.     

Novel stereoselective synthesis of 2,3-dihydro-1H-benzo[f]chromen-3-amine derivatives through a one-pot three-component reaction

A short and stereoselective novel synthesis of benzo[f]chromen-3-amine derivatives in good yields, through a three-component aromatic Betti type reaction under solvent free conditions is reported. The spontaneous reaction occurs in the absence of acid catalysts. The use of chiral 1-phenylethylamine or α,β-unsaturated aldehydes allowed us to prepare enantiopure benzo[f]chromen-3-amine derivatives with good stereoselectivity. Conformational analysis compared with the ¹H NMR data of the products obtained, allowed us to the determine the absolute configuration, which was also confirmed by X-ray analysis.     

InCl3-promoted a novel Prins cyclization for the synthesis of hexahydro-1H-furo[3,4-c]pyran derivatives

(2-(4-Methoxyphenyl)-4-methylenetetrahydrofuran-3-yl)methanol reacts smoothly with different aldehydes in the presence of InCl₃ at an ambient temperature to afford a novel series of cis-fused 7a,3,6-trisubstituted hexahydro-1H-furo[3,4-c]pyran derivatives in good yields with high selectivity. This is the first Letter on the synthesis of cis-fused hexahydro-1H-furo[3,4-c]pyran derivatives via the Prins cyclization.     

Aminol initiated Prins cyclization for the synthesis of octahydro-1H-pyrano [3,4-c]pyridine and hexahydro-1H-furo[3,4-c]pyrrole derivatives

Various aldehydes undergo smooth coupling with a branched homoallylic alcohol appended N-tosyl amine (1 & 3) in the presence of 10 mol % BF₃·OEt₂ at room temperature to afford a novel class of 1,8-disubstituted octahydropyrano[3,4-c]pyridine and 1,6-disubstituted hexahydrofuro[3,4-c]pyrrole derivatives in good yields, respectively.     

New synthesis of 3-amino-1H-benzo[f]chromene-2-carbonitriles

3-Amino-1H-benzo[f]chromene-2-carbonitriles were synthesized by non-catalytic reaction from Mannich bases of the naphthalene series and malononitrile. Reactive 1-benzylidene(or methylidene)naphthalen-2(1H)-ones were presumed as intermediate products.     

The stereoselective synthesis of cis-/trans-fused hexahydropyrano[4,3-b]chromenes via Prins cyclization trapping by a tethered nucleophile

A novel intramolecular Prins cyclization of (Z)-2-(5-hydroxypent-2-enyl)phenol with various aldehydes has been achieved using 10 mol% In(OTf)(3) and 30 mol% TsOH to produce the cis-fused hexahydropyrano[4,3-b]chromene derivatives in good yields, while the coupling of (E)-2-(5-hydroxypent-2-enyl)phenol with aldehydes under similar conditions affords the corresponding trans-fused hexahydropyrano[4,3-b]chromene derivatives.     

The stereoselective total synthesis of xestodecalactone C and epi-sporostatin via the Prins cyclisation

Syntheses of xestodecalactone C and epi-sporostatin are described utilising Prins cyclisations, Mitsunobu reaction and intramolecular Friedel-Crafts acylation. The approach is convergent and highly stereoselective.     

Oxa-[3+3] annulation of 1H-benzo[f]chromene-2-carbaldehydes and 2-naphthols: synthesis of 7aH,15H-benzo[f]benzo[5,6]chromeno[2,3-b]chromenes

Chemistry of Heterocyclic Compounds - A method for the preparation of polycondensed chromeno[2,3-b]chromenes was developed based on the formal [3+3] cycloaddition reaction between...     

InBr3-catalyzed stereoselective synthesis of 3,4-disubstituted hexahydro-1H-furo[3,4-c]pyran derivatives

An ?,δ-unsaturated alcohol tethered with a hydroxyl group, that is, (E)-2-styrylbutane-1,4-diol (1) undergoes a smooth bicyclization with various aldehydes in the presence of 10 mol % InBr₃ and at 0 °C to afford a novel series of hexahydro-1H-furo[3,4-c]pyran derivatives in good yields with high diastereoselectivity.     

A novel Prins reaction for the synthesis of hexahydro-8,8-dimethyl-1H-isochromen-7-ol derivatives

Various aldehydes undergo smooth coupling with 5-(hydroxymethyl)-4,6,6-trimethylcyclohex-3-enol in the presence of p-TSA at ambient temperature to afford a novel series of hexahydro-8,8-dimethyl-1H-isochromen-7-ol derivatives in good yields with high selectivity. This is the first report on the synthesis of isochromen-7-ol derivatives via the Prins reaction.     

Intramolecular Prins cyclisations for the stereoselective synthesis of bicyclic tetrahydropyrans

Methyl (4E,7R)-7-hydroxyoctanoate was prepared in 71% yield from ethyl (R)-3-hydroxybutanoate and on reaction with a series of aldehydes in the presence of TMSOTf gave bicyclic oxygen heterocycles in good yields and with the creation of three new stereogenic centres in a single pot.     

Efficient one-pot synthesis of 1,3-diaryl-3H-benzo[f]chromenes using ferric hydrogensulfate

<正>An efficient and easy method for one-pot three-component synthesis of l,3-disubstituted-3H-benzo[f]chromenes by the condensation of naphtol,aromatic aldehyde derivatives and phenylacetylene in the presence of ferric hydrogensulfate[Fe(HSO_4)_3], has been described.The catalyst displayed high activity which afforded the corresponding 1,3-disubstituted-3H-benzo[f]chromenes in satisfying yields.Alkyl-substituted phenols were examined and the corresponding benzopyran derivatives were synthesized in moderate yields.Heterogeneous nature of the using catalyst made it reusable for further chemical reactions.     

A concise stereoselective formal total synthesis of the cytotoxic macrolide (+)-Neopeltolide via Prins cyclization

A convergent and highly stereoselective formal total synthesis of the naturally occurring, cytotoxic 14-membered macrolide neopeltolide has been achieved via two Prins cyclizations.     

Direct C-N coupling of imidazoles and benzylic compounds via iron-catalyzed oxidative activation of C-H bonds

Iron-catalyzed direct C-N bond formation between imidazoles and benzylic hydrocarbons is described. The reaction utilizes an inexpensive iron catalyst-oxidant system that is suitable for the coupling of a range of benzylic C-H bonds with various imidazoles.     

Studies on the Michael addition of naphthoquinones to sugar nitro olefins: first synthesis of polyhydroxylated hexahydro-11H-benzo[a]carbazole-5,6-diones and hexahydro-11bH-benzo[b]carbazole-6,11-diones

A strategy for the synthesis of the novel (6bR,7R,8S,9S,10S,10aR)-8-(benzyloxy)-7,9,10-trihydroxy-6b,7,8,9,10,10a-hexahydro-11H-benzo[a]carbazole-5,6-dione is reported. The key steps were the Michael addition of 2-hydroxy-1,4-naphthoquinone to 1-nitrocyclohexene or 3-O-benzyl-5,6-dideoxy-1,2-O-isopropylidene-6-nitro-α-d-xylo-hex-5-enefuranose and the diastereoselective intramolecular Henry reaction of 3-O-benzyl-5,6-dideoxy-5-C-(3′-hydroxy-1′,4′-naphthoquinon-2′-yl)-1,2-O-isopropylidene-6-nitro-α-d-glucofuranose to give the key (1S,2S,3S,4R,5R,6R)-3-(benzyloxy)-1,2,4-trihydroxy-5-(3′-hydroxy-1′,4′-naphthoquinon-2′-yl)-6-nitrocyclohexane. When 2-hydroxy-1,4-naphthoquinone was replaced by (1,4-dimethoxynaphthalen-2-yl)lithium, the novel (1R,2S,3S,4R,4aS,11bS)-2-(benzyloxy)-1,3,4-trihydroxy-1,2,3,4,4a,5-hexahydro-11bH-benzo[b]carbazole-6,11-dione was obtained.     

Montmorillonite KSF-catalyzed one-pot synthesis of hexahydro-1H-pyrrolo[3,2-c]quinoline derivatives

Aryl amines react with endocyclic ene-carbamates such as tert-butyl 2,3-dihydro-1H-1-pyrrolecarboxylate and tert-butyl 1,2,3,4-tetrahydro-1-pyridinecarboxylate, on the surface of montmorillonite KSF clay under mild conditions to afford the corresponding 3-aminopropylhexahydropyrrolo[3,2-c]quinoline or 4-aminobutyloctahydrobenzo[h][1,6]naphthyridine derivatives in excellent yields with moderate diastereoselectivity.     

Rhodium catalyzed synthesis of isoindolinones via C-H activation of N-benzoylsulfonamides

An efficient approach to a wide range of isoindolinones, including 3-monosubstituted and 3,3-disubstituted isoindolinones, from the annulation of N-benzoylsulfonamides with olefins and diazoacetate has been developed. The transformation is broadly compatible with both terminal and internal olefins. Moreover, diazoacetate is for the first time incorporated into an amide-directed C-H functionalization reaction. Specifically, the rhodium complex [{RhCl₂Cp*}₂] enables the in situ dimerization of diazoacetate in addition to its role in catalyzing C-H functionalization/cross-coupling.     

Highly stereoselective synthesis of tetrasubstituted alkenes via hydroamination of alkynes and C-H acetoxylation

A novel reaction including the sequence of hydroamination of alkynes and subsequent oxidative C-H bond functionalization has been developed in the presence of diacetoxyiodobenzene (DIB). The method allows us to synthesize a wide range of tetrasubstituted (E)-alkenes and provides a potential method to construct densely functionalized carbonyl compounds.     

Generation of 4-polyfluoroaryl pyrrolo[1,2-a]quinolines via C-H bond activation

A novel and efficient preparation of 4-polyfluoroaryl pyrrolo[1,2-a]quinolines via a palladium-catalyzed reaction of 1-[2-(2,2-dibromoethenyl)phenyl]-1H-pyrrole with polyfluoroarene is described. This transformation is efficient, leading to the corresponding products in good yields.     

A cycloisomerization/Friedel-Crafts alkylation strategy for the synthesis of pyrano[3,4-b]indoles

The synthesis of pyrano[3,4-b]indoles is described. The reaction sequence involves Sonogashira coupling of dihydropyran propargyl ether scaffolds with iodoanilines to afford intermediate indoles. Lewis acid-catalyzed ionization of the dihydropyrans, followed by intramolecular C3 alkylation of the indole, provides the title compounds.