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Highly torquoselective electrocyclizations of chiral 1-azatrienes are described. These 1-azatrienes contain an allylic stereocenter that is substituted with a silyl group and are derived in situ from condensation of γ-silyl-substituted enals with vinylogous amides. The ensuing stereoselective ring closures are part of a tandem sequence that constitutes an aza-[3 + 3] annulation method for constructing 1,2-dihydropyridines. Several mechanisms for the formal 1,7-hydrogen shift of these 1-azatrienes were evaluated computationally.

We report the first experimental evidence for the generation of highly strained cis,trans-cycloheptadienones by electrocyclic ring opening of 4,5-fused cyclobutenamides. In the presence of AlCl3, the cyclobutenamides rearrange to [2.2.1]-bicyclic ketones; DFT calculations provide evidence for a mechanism involving torquoselective 4π-electrocyclic ring opening to a cis,trans-cycloheptadienone followed by a Nazarov-like recyclization and a 1,2-alkyl shift. Similarly, 4,6-fused cyclobutenamides undergo AlCl3-catalyzed rearrangements to [3.2.1]-bicyclic ketones through cis,trans-cyclooctadienone intermediates. The products can be further elaborated via facile cascade reactions to give complex tri- and tetracyclic molecules.

Electrocyclic ring opening of 4,6-fused cyclobutenamides 1 under thermal conditions leads to cis,trans-cyclooctadienones 2-E,E as transient intermediates, en route to 5,5-bicyclic products 3. Theoretical calculations predict that 4,5-fused cyclobutenamides should likewise undergo thermal ring opening, giving cis,trans-cycloheptadienones, but in this case conversion to 5,4-bicyclic products is thermodynamically disfavored, and these cyclobutenamides instead rearrange to vinyl cyclopentenones.

Computer-aided design and computer-aided manufacturing (CAD-CAM) technology has greatly improved the efficiency of the fabrication of dental prostheses. However, the design process (CAD stage) is still time-consuming and labor intensive. The purpose of this feasibility study was to investigate the accuracy of a novel artificial intelligence (AI) system in designing biomimetic single-molar dental prostheses by comparing and matching them to the natural molar teeth. A total of 169 maxillary casts were obtained from healthy dentate participants. The casts were digitized, duplicated, and processed with the removal of the maxillary right first molar. A total of 159 pairs of original and processed casts were input into the Generative Adversarial Networks (GANs) for training. In validation, 10 sets of processed casts were input into the AI system, and 10 AI-designed teeth were generated through backpropagation. Individual AI-designed teeth were then superimposed onto each of the 10 original teeth, and the morphological differences in mean Hausdorff distance were measured. True reconstruction was defined as correct matching between the AI-designed and original teeth with the smallest mean Hausdorff distance. The ratio of true reconstruction was calculated as the Intersection-over-Union. The reconstruction performance of the AI system was determined by the Hausdorff distance and Intersection-over-Union. Data of validation showed that the mean Hausdorff distance ranged from 0.441 to 0.752 mm and the Intersection-over-Union of the system was 0.600 (60%). This study demonstrated the feasibility of AI in designing single-molar dental prostheses. With further training and optimization of algorithms, the accuracy of biomimetic AI-designed dental prostheses could be further enhanced. [ABSTRACT FROM AUTHOR]

Rhodium(I) catalyzed [2@@] cycloadditions of sterically encumbered aryl-substituted ynamides with various diynes are described. These cycloadditions provide the synthesis of an array of new chiral amide-substituted biaryls that can be useful for chiral ligand designs.

A general and efficient method for the coupling of a wide range of amides with alkynyl bromides is described. This novel amidation reaction involves a catalytic protocol using copper(II) sulfate-pentahydrate and 1,10-phenanthroline to direct the sp-C-N bond formation, leading to a structurally diverse array of ynamides including macrocyclic ynamides via an intramolecular amidation.

Detailed investigation of formal aza- [3+3] cycloaddition reactions of tetronamides with alpha, beta-unsaturated iminium salts is presented. Interesting regioisomeric cycloadducts involving related formal aza- [3+3] cycloadditions and unexpected rearrangements that led to pyridine and 1,2-dihydropyridine products were uncovered in this investigation.

Tests show that a highly stereoselective 6(Pi)-electron electrocyclic ring closure of 1-azatrienes is a major step in formal [3 + 3] cycloaddition or annulation of chiral vinylogous amides with alpha, beta-unsaturated iminium salts. It is seen that fluorous mixture synthesis is a unique solution-phase high throughput technique that allows production of many more compounds from a synthetic exercise.

Research demonstrates a formal [3+3] cycloaddition approach for the preparation of the title compounds, the pyranoquinoline alkaloids, using alpha,beta-unsaturated iminiums and 4-hydroxy-2-quinolones. The substitutions are on the pyranyl ring.

A synthesis of 3-cyano-4-benzopyrone derivatives by acid-promoted elimination of O-methyl oximes has been reported. The authors examine procedures that describe preparations from the aldehydes through oxime intermediates.

Reactions between amino-stabilized alpha,beta-unsaturated Fischer carbene complexes and alkynes resulted in the formation of phenols. The selectivity of phenols increases at high concentration and by using noncoordinating solvents. Low yield of phenols were obtained from internal alkynes whereas terminal alkynes in the presence of trapping agent produced good yield of 4-(dimethylamino)phenols.

A de novo preparation of [alpha]-keto-imide by using ynamide oxidation is described. Chemoselective oxidation of ynamides containing olefins is achieved by using DMDO, while the Ru[O.sub.2]-NaI[O.sub.4] protocol is not very effective.

The stereoselective synthesis of the C1-C9 subunit of (+)-zincophorin is described. The unusual urea-directed Stork-Crabtree hydrogenation is observed during the total synthesis.