A New Synthesis of Benzylidene Acetals

Aryl-halo-diazirines react under basic conditions with 1,3-cis-, 1,2-cisand 1,2-trans-diols to give acetals. Yields are high. Diastereoselectivities depend upon the diol and upon the reaction conditions. Thus, reaction of the 1,3-cis-diol 1 (Scheme 1) with 2 gave 3 as a single diastereoisomer. The 1,2-cis-diols 4 and 7 led to the endo- and exo-acetals 5 / 6 (93:7) and 8 / 9 (ca.10:1), respectively, The 1,2-trans-diols 10 , 16 , and 19 reacted with 2 to afford 11 / 12 (90:10), 17 / 18 (1:1), and 20 / 21 (6:1), respectively. Reaction of the (4-nitrophenyl)diazirine 13 with 10 at higher temperatures yielded 14 / 15 (6:4). The uracil moiety, the acetamido group, and the enol-ether moiety are compatible with the reaction conditions. The diastereoselectivity is rationalized on the basis of a reaction sequence involving alkoxy-halogen exchange, which is regioselective or not, thermolysis of the ensuing alkoxydiazirine(s), protonation of the alkoxycarbene to form an (E)-configurated oxycarbenium ion, and attack of the neighboring oxy or hydroxy group, which is only possible for a limited range of conformers.     

Practical,Modular, and General Synthesis of Benzofurans through Extended Pummerer Annulation/Cross‐Coupling Strategy

Operationally simple, efficient, and widely applicable Pummerer annulations of simple phenols with ketene dithioacetal monoxides, with the aid of trifluoroacetic anhydride, have been shown to provide a variety of benzofurans having a methylthio group at the 2‐position. Subsequent and newly developed nickel‐catalyzed arylation at the methylthio group culminates in diversity‐oriented synthesis of multisubstituted benzofurans. Our extended Pummerer annulation/cross‐coupling sequence is powerful enough to synthesize biologically active natural products as well as highly fluorescent benzofuran derivatives.     

Practical,Modular, and General Synthesis of Benzofurans through Extended Pummerer Annulation/Cross‐Coupling Strategy

Operationally simple, efficient, and widely applicable Pummerer annulations of simple phenols with ketene dithioacetal monoxides, with the aid of trifluoroacetic anhydride, have been shown to provide a variety of benzofurans having a methylthio group at the 2‐position. Subsequent and newly developed nickel‐catalyzed arylation at the methylthio group culminates in diversity‐oriented synthesis of multisubstituted benzofurans. Our extended Pummerer annulation/cross‐coupling sequence is powerful enough to synthesize biologically active natural products as well as highly fluorescent benzofuran derivatives.     

A Short and Simple Synthesis of Ketene Acetals

A novel and convenient synthesis of ketene acetals 1a-g in moderate to good yield has been achieved starting from acetonitrile by using Pinner reaction approach.     

Metal‐Free One‐Pot Synthesis of Benzofurans

Ethyl acetohydroxamate was efficiently arylated with diaryliodonium salts at room temperature under transition‐metal‐free conditions. The obtained O‐arylated products were reacted in situ with ketones under acidic conditions to yield substituted benzo[b]furans through oxime formation, [3,3]‐rearrangement, and cyclization in a fast and operationally simple one‐pot fashion without using excess reagents. Alternatively, the O‐arylated products could be isolated or transformed in situ to aryloxyamines or O‐arylaldoximes. The methodology was applied to the synthesis of Stemofuran A and the formal syntheses of Coumestan, Eupomatenoid 6, and (+)‐machaeriol B.     

A General Synthesis of Alkenyl‐Substituted Benzofurans,Indoles, and Isoquinolones by Cascade Palladium‐Catalyzed Heterocyclization/Oxidative Heck Coupling

Structurally diverse C3‐alkenylbenzofurans, C3‐alkenylindoles, and C4‐alkenylisoquinolones are efficiently prepared by using consecutive Sonogashira and cascade Pd‐catalyzed heterocyclization/oxidative Heck couplings from readily available ortho‐iodosubstituted phenol, aniline, and benzamide substrates, alkynes, and functionalized olefins. The cyclization of O‐ and N‐heteronucleophiles follows regioselective 5‐endo‐dig‐ or 6‐endo‐dig‐cyclization modes, whereas the subsequent Heck‐type coupling with both mono‐ and disubstituted olefins takes place stereoselectively with exclusive formation of the E isomers in most cases.     

DABCO-Promoted Efficient and Convenient Synthesis of Benzofurans

An efficient and convenient synthesis of benzofurans has been described from phenacyl halides and o-hydroxy benzaldehyde in the presence of DABCO. The procedure is applicable for a variety of phenacyl halides and provide a variety of benzofurans. DABCO act as a base and as well as nucleophile.     

A Simple Synthesis of 3-Nitrocycloalkenones and their Acetals

Synthesis of 3-nitrocyclohexenone and 3-nitrocycloheptenone and their acetals in described starting from cyclohexanone and cycloheptanone respectively.     

Direct Synthesis of N-Arylquinone Imine Acetals and Quinol Imines from Acetals

In the absence of any added acidic catalyst quinone acetals as well as simple ketone and aldehyde acetals react with a variety of substituted anilines to form imines [Eq. (a)]. Contrary to what is expected from arguments based on their nucleophilicity, the most reactive anilines are those bearing electron-withdrawing groups.     

Novel and Convenient Synthesis of Benzofurans from Dihydrocoumarins

7‐Hydroxy‐3,4‐dihydrocoumarin‐4‐carboxylic acid ( 7 ), conveniently prepared from m‐resorcinol and maleic anhydride, was surprisingly transformed by acid anhydride and pyridine into the corresponding ketone, 4‐alkanoyl analog 11 . The latter reacted in turn with acidic alcohol yielding benzofuran‐3‐yl‐acetic ester 16.     

A New Synthesis of Benzofurans from Phenols via Claisen Rearrangement and Ring‐Closing Metathesis

Based on Claisen rearrangement, the double bond isomerization of O‐allyl function together with the formation of O‐vinyl function in one pot, and ring‐closing metathesis (RCM), various phenols were transformed into various benzofurans in good yields.     

Synthesis of Arylated Benzofurans by Regioselective Suzuki–Miyaura Cross‐Coupling Reactions of 2,3‐Dibromobenzofurans‐ and 2,3,5‐Tribromobenzofurans

Arylated benzofurans were prepared by regioselective Suzuki–Miyaura cross‐coupling reactions of 2,3‐dibromobenzofuran. The reactions proceeded with very good site‐selectivity in favor of the more electron deficient position 2. The Suzuki–Miyaura reactions of 2,3,5‐tribromobenzofuran also proceeded in favor of position 2.     

Functionalized Benzofurans via Microwave‐Promoted Tandem Claisen‐Rearrangement/5‐endo‐dig Cyclization

Ortho‐allyloxy alkinyl benzenes undergo, upon microwave irradiation in dimethylformamide, a tandem sequence of Claisen‐rearrangement and 5‐endo‐dig cyclization to furnish 7‐allyl‐substituted benzofurans. With terminal alkynes, chroman‐4‐ones and enaminoketones become the main products. A mechanistic proposal for this observation relies on a reaction of the starting material with the solvent dimethylformamide under the microwave conditions.     

A Base-Mediated Approach Towards Dihydrofuro[2,3-b]Benzofurans from 2-Nitrobenzofurans and 1,3-Dicarbonyls

A straight-forward approach for the synthesis of a dihydrofuro[2,3-b]benzofuran derivatives has been achieved through a base-mediated Michael addition of 1,3-dicarbonyls to 2-nitrobenzofurans followed by intramolecular cyclization. A variety of 1,3-dicarbonyls, including cyclic as well as trifluoromethylated ones, have been subjected to react with 2-nitrobenzofurans under optimal conditions, and the respective dihydrofuro[2,3-b]benzofurans could be accessed in moderate to excellent yields.     

Synthesis of 2,3‐Disubstituted 5‐Iodo‐1H‐Pyrrolo[2,3‐b]pyridines via Fischer Cyclization

A simple and convenient procedure for the preparation of some unknown 2,3‐disubstituted 5‐iodo‐1H‐pyrrolo[2,3‐b ]pyridines from readily available starting materials by Fischer indole cyclization in polyphosphoric acid is described. The present methodology provides an alternative synthetic approach to the synthesis of 5‐iodo‐7‐azaindole scaffold. All synthesized compounds were characterized by IR, MS, ¹H and ¹³C NMR, and elemental analysis.     

Novel Synthesis of Benzosubstituted Benzofurans Via Diels-Alder Reaction

A useful synthetic approach to benzosubstltuted benzofurans via Diels-Alder reaction of 2-vinyl furans is described.     

三甲基溴代硅烷促进的非环状与环状缩醛(酮)的合成

以三甲基溴代硅烷作为反应促进剂, 在室温和原甲酸酯或原乙酸酯存在的条件下, 利用醇、二醇处理羰基化合物, 高收率地实现了一系列非环状与环状缩醛(酮)的合成. 产物结构经1H NMR、元素分析等进行了表征.