Annulation Strategy Research Articles

A [4+4] annulation strategy for the synthesis of eight-membered carbocycles based on intramolecular cycloadditions of conjugated enynes

A [4+4] annulation strategy for the synthesis of eight-membered carbocycles is reported that proceeds via a cascade involving two pericyclic processes. In the first step, the [4+2] cycloaddition of a conjugated enyne with an electron-deficient cyclobutene generates a strained six-membered cyclic allene that isomerizes to the corresponding 1,3-cyclohexadiene. In the second step, this bicyclo[4.2.0]octa-2,4-diene intermediate undergoes thermal or acid-promoted 6-electron electrocyclic ring opening to furnish a 2,4,6-cyclooctatrienone. The latter transformation represents the first example of the promotion of 6-electron electrocyclic ring opening reactions by acid.

Stepwise Fusion of Porphyrin β,β′-Pyrrolic Positions to Imidazole Rings

A strategy for the stepwise annulation of pyrrolic rings of a porphyrin to imidazole rings is presented. Mono(imidazole), Janus and corner bis(imidazole), T-shaped tris(imidazole), and tetrakis(imidazole) porphyrins have been synthesized and characterized.

Synthesis of Carbazole‐Containing Porphyrinoids by a Multiple Annulation Strategy: A Core‐Modified and π‐Expanded Porphyrin

Synthesis of Carbazole‐Containing Porphyrinoids by a Multiple Annulation Strategy: A Core‐Modified and π‐Expanded Porphyrin

Synthesis of Carbazole‐Containing Porphyrinoids by a Multiple Annulation Strategy: A Core‐Modified and π‐Expanded Porphyrin

Synthesis of Carbazole‐Containing Porphyrinoids by a Multiple Annulation Strategy: A Core‐Modified and π‐Expanded Porphyrin

5+1]-Annulation Strategy Based on Alkenoyl Ketene Dithioacetals and Analogues

Functionalized ketene dithioacetals are versatile intermediates in organic synthesis. The important multiple roles of the dialkylthio group make these substrates particularly useful for the synthesis of a number of important classes of substituted carbo- and heterocyclic systems, such as thiophenes, lactones, pyrroles, furans, pyridines, substituted cyclohexanones, and benzene derivatives. This account focuses on the utility of alkenoyl ketene dithioacetals, which have been found useful in the synthesis of six-membered carbo- and heterocyclic systems relying upon utilization of alkenoyl ketene dithioacetals, as the 1,5-bielectrophilic component in the [5+1] annulation with carbon, nitrogen, sulfur, and other nucleophiles.

Dynamic Kinetic Asymmetric Synthesis of Five Contiguous Stereogenic Centers by Sequential Organocatalytic Stetter and Michael−Aldol Reaction: Enantioselective Synthesis of Fully Substituted Cyclopentanols Bearing a Quaternary Stereocenter

A synthesis of fully substituted cyclopentanes bearing a quaternary carbon center and five contiguous stereogenic centers has been achieved by sequential organocatalyzed Stetter and Michael-Aldol reactions of heteroaromatic aldehydes, nitroalkenes, and α,β-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with dynamic kinetic asymmetric transformation and excellent enantioselectivities (up to >99% ee).

ChemInform Abstract: Sequential Organocatalytic Stetter and Michael‐Aldol Condensation Reaction: Asymmetric Synthesis of Fully Substituted Cyclopentenes via a [1 + 2 + 2] Annulation Strategy.

AbstractThe method consists of the preparation of the β‐nitroketones using thiazolium catalyst [cf.

Asymmetric organocatalytic [3 + 2]-annulation strategy for the synthesis of N-fused heteroaromatic compounds

Hydroxyalkyl- or aminoalkyl-substituted N-fused heteroaromatic compounds can be efficiently accessed via an organocatalytic [3 + 2]-annulation strategy. The developed cascades proceed in a highly enantioselective manner and benefit from broad substrate scope, operational simplicity, easily available starting materials as well as low catalyst loadings.

Iron-Mediated [3 + 2] or [3 + 3] Annulation of 2-(2-(Ethynyl)phenoxy)-1-arylethanones: Selective Synthesis of Indeno[1,2-c]chromenes and 5H-Naphtho[1,2-c]chromenes

An iron-mediated tandem annulation strategy has been developed for the synthesis of numerous functional indeno[1,2-c]chromenes and 5H-naphtho[1,2-c]chromenes. This work is the first to disclose an iron-mediated method through sequential electrophilic addition of a ketone to an alkyne and annulation tandem reaction. Importantly, a halide is introduced into the products by a ring-opening process among the annulation of alkynylcyclopropanes, which makes the methodology more attractive for organic synthesis.

Catalytic Asymmetric Formal [4 + 1] Annulation Leading to Optically Active cis-Isoxazoline N-Oxides

The catalytic asymmetric synthesis of densely functionalized cis-isoxazoline N-oxides was realized with novel use of an organocatalyst, (S)-2-(azidodiphenylmethyl)pyrrolidine (4e) (Tan, B.; Zhu, D.; Zhang, L.; Chua, P. J.; Zeng, X.; Zhong, G. Chem.-Eur. J. 2010, 16, 3842; Olivares-Romero, J. L.; Juaristi, E. Tetrahedron 2008, 64, 9992), via an elegant formal [4 + 1] annulation strategy using readily available 2-nitroacrylates and α-iodoaldehydes.

Sequential Organocatalytic Stetter and Michael-Aldol Condensation Reaction: Asymmetric Synthesis of Fully Substituted Cyclopentenes via a [1 + 2 + 2] Annulation Strategy

A stereoselective synthesis of fully substituted cyclopentenes has been achieved by a sequential organocatalyzed Stetter and Michael-aldol condensation of aromatic aldehydes, nitroalkenes, and α,β-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with excellent diastereoselectivities and enantioselectivities (up to >99% ee).

Cover Picture: Iron-Catalyzed Carbonylation as a Key Step in the Short and Efficient Syntheses of Himanimide A and B (Chem. Asian J. 10/2010)

An iron–catalyzed [2+1+1+1]–annulation strategy was used for the construction of five–membered maleimides, which are building blocks for naturally occurring himanimides A and B. In their Communication on page 2173 ff., M. Beller et al. report that the syntheses of himanimide A and B are conveniently achieved in only 4 and 5 steps from commercially available starting materials, respectively. Whilst himanimide B was prepared for the first time, the synthesis of himanimide A has been significantly improved with respect to overall yield. This synthetic strategy can be applied to other related bio–active compounds, such as camphorataimides, antrocinnamomins, polycitrins, and arcyriarubins.

ChemInform Abstract: A Novel and Efficient Synthesis of 4H-3,1-Benzoxazines by a Tandem Aza- Wittig/Heterocumulene-Mediated Annulation Strategy.

2-[(Triphenylphosphoranylidene)amino]benzyl alcohol 2 reacts with isocyanates or isothiocyanates in refluxing toluene to give the corresponding 2-alkyl(aryl)amino-4H-3,1-benzoxazines 5. Iminophosphorane 2 also reacts with carbon dioxide and carbon disulfide to give 4H-3,1-benzoxazin-2(1H)-one (6) and -thionine (7), respectively

ChemInform Abstract: Highly Diastereoselective Anionic (3 + 2) Annulation Strategy for Functionalized Cyclopentenes via α-Oxoketene Dithioacetals.

ChemInform Abstract: Highly Diastereoselective Anionic (3 + 2) Annulation Strategy for Functionalized Cyclopentenes via α-Oxoketene Dithioacetals.

Aza-[3 + 3] Annulations: A New Unified Strategy in Alkaloid Synthesis.

An aza-[3 + 3] annulation or formal cycloaddition strategy for constructing complex heterocycles, chiefly alkaloids, is reviewed here. This annulation involves a Knoevenagel-type condensation of α,β-unsaturated iminium salts with vinylogous amides or urethanes followed by a 6π-electron electrocyclic ring-closure. Both the inter- and intramolecular aza-annulation pathways illustrated here constitute a stepwise formal [3 + 3] cycloaddition in which two -bonds are formed in addition to a new stereogenic center adjacent to the heteroatom. This review describes our total synthesis efforts in the last ten years to unequivocally demonstrate that this aza-[3 + 3] annulation can serve as a powerful approach and a unified strategy in alkaloid synthesis. Keywords: Alkaloid synthesis, Aza-[3 + 3] annulation, Formal cycloaddition, Heterocycle, A unified synthetic strategy

Iron‐Catalyzed Carbonylation as a Key Step in the Short and Efficient Syntheses of Himanimide A and B

Isn't it iron-ic: An iron-catalyzed [2+1+1+1]-annulation strategy is used for the construction of five-membered maleimides, which are building blocks for naturally occurring himanimides A and B.

ChemInform Abstract: Facile and Efficient Synthesis of Hydrophenanthren‐1(2H)‐ones and Naphtho[2,1‐c]furan‐3(1H)‐ones by a Palladium‐Catalyzed Aryne Annulation Strategy.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Organocatalytic Tandem Reaction to Construct Six‐Membered Spirocyclic Oxindoles with Multiple Chiral Centres through a Formal [2+2+2] Annulation

An efficient tandem reaction for the asymmetric synthesis of six-membered spirocyclic oxindoles has been successfully developed through a formal [2+2+2] annulation strategy. The amine-catalysed stereoselective Michael addition of aliphatic aldehydes to electron-deficient olefinic oxindole motifs gave chiral C3 components, which were further combined with diverse electrophiles (activated olefins or imines) to afford spirocyclic oxindoles with versatile molecular complexity (up to six contiguous stereogenic centres, high diastereo- and enantioselectivities).

Facile and Efficient Synthesis of Hydrophenanthren‐1(2H)‐ones and Naphtho[2,1‐c]furan‐3(1H)‐ones by a Palladium‐Catalyzed Aryne Annulation Strategy

AbstractNovel palladium‐catalyzed carboannulation reactions of arynes with functionalized vinyl iodides are reported. By applying allyl‐substituted iodocycloenones and iodofuranones, a series of hydrophenanthren‐1(2H)‐ones and naphtho[2,1‐c]furan‐3(1H)‐ones were efficiently constructed in one pot under mild conditions.

An efficient stereoselective synthesis of 3-spirocyclopentene- and 3-spiropyrazole-2-oxindoles via 1,3-dipolar cycloaddition reaction

The chemistry phosphorus and sulfur ylides have been exploited for a facile, short and efficient synthesis of 3-spirocyclopentene- and 3-spiropyrazole-2-oxindoles from E- and Z-isomers of bromo derivatives of Morita-Baylis-Hillman adducts of isatin with Ph(3)P/activated alkene/K(2)CO(3) and Me(2)S/DEAD/K(2)CO(3), respectively, via [3 + 2]-annulation strategy.