A tandem 1,6-addition/cyclization/vinylcyclopropane rearrangement reaction (VCPR) of vinylogous para-quinone methides at low temperature under metal-free conditions has been disclosed for the first time. This method provides an efficient strategy for the construction of a range of spiro[4.5]cyclohexadienones in good yield, exhibiting good functional group tolerance as well as gram-scale capacity.

An efficient one-pot approach for the synthesis of spiro[2.5]octa-4,7-dien-6-ones by employing para-quinone methides has been developed. The reaction proceeded smoothly in high yields under mild conditions without the use of metals. Moreover, all products obtained herein contained two or three consecutive quaternary centers.

F ull crowns have long been the most common choice for treatment of unesthetic anterior teeth caused by discoloration, defects, or malformation. However, this treatment causes extensive loss of sound tooth substance. 1 Minimally invasive treatments have become possible due to the development of acid etching and bonding techniques. One of these options is veneer restorations (VRs). The most commonly used VRs can be divided into three categories: direct resin VRs, indirect resin VRs, and porcelain laminate VRs. 2 Clinically, porcelain laminate and indirect resin VRs are more popular than direct resin VRs due to shorter chairside operating time and more ideal edge shapes. Additionally, unlike direct resin VRs, the indirect resin and porcelain VRs share similar repair processes that involve tooth preparation, veneer fabrication, and cementation. With the widespread application of indirect resin and porcelain laminate VRs, their longevities have become a focus of attention. Purpose: To evaluate and compare the failure and complication risks of porcelain laminate and indirect resin veneer restorations (VRs) by means of a meta-analysis. Methods: An electronic database search was performed in MEDLINE (PubMed), EMBASE (Ovid), and the Cochrane Central Register of Controlled Trials (CENTRAL) databases, and a gray literature search was performed on OpenGrey. All database searches were completed by March 2018. Two authors individually screened the literature according to the inclusion and exclusion criteria. The quality and risk of bias of the included studies were evaluated using the Newcastle-Ottawa scale (NOS) and the Cochrane Handbook for Systematic Reviews of Interventions (CHSRI). The Mantel-Haenszel method was used to synthesize the data of the included studies. All statistical analyses were performed using the software Stata 14.0, and the results were expressed as risk ratio (RR) with 95% confidence interval (CI). Results: Five studies-two randomized controlled trials (RCTs) and three clinical controlled trials (CCTs)-were included in this review. Of the three CCTs, two were assessed to be low quality, and the third was considered high quality. The two RCTs were rated as unclear risk of bias. The meta-analysis results showed the risk of failure for indirect resin VRs was higher than for porcelain laminate VRs (RR: 0.15, 95% CI: 0.06-0.40; P = .000). Fracture and debonding were the main complications leading to failure. For risk of fracture, an RR of 0.18 (95% CI: 0.04-0.71) and a statistically significant difference (P = .015) were found in favor of porcelain laminate VRs. For risk of debonding, there was no statistically significant difference (P = .108) found between the two types of VRs. The results of the sensitivity analysis (RR: 0.09, 95% CI: 0.02-0.45; P = .004) suggested that this conclusion was reliable. Conclusion: The survival rate of porcelain laminate VRs was higher than indirect resin VRs, and the latter had a higher risk of fracture. However, there was no statistically significant difference in the risk...

An unprecedented [4+ +2] cycloaddition of in situ generated azoalkenes with arylacetic acids has been developed under the catalysis of isothiourea. Ther eaction provideda ne fficienta pproacht o the synthesis of 4,5-dihydropyridazin-3(2H)-one derivatives in moderate to good yields(up to 95%).Keywords: 1,2-diaza-1,3-dienes;4 ,5-dihydropyridazin-3(2H)-ones;i sothioureacatalysis Dihydropyridazinones and pyridazinones are important six-membered aza-heterocycles,a nd are present in aw ide range of bioactive compoundsw ith anti-inflammatory, [1] anti-platelet aggregation [2] and anti-congestive heart failurea ctivities (Figure 1). To the best of our knowledge, the reported synthetic strategies for the synthesiso fd ihydropyridazinones are normally limited to the condensation of costly substrate goxo acids andh ydrazine.[3] Therefore,t he development of an ew strategyt hat allowsr apid access to dihydropyridazinones from readily accessible starting materials using ap ractical method is still highly desirable and an enduring goal of organic chemistry.Organocatalysis is now aw elle stablished instrument in the organic chemists tool box due to the generally stability,h igh quality,i nexpensive price, and lower toxicity compared to transitionm etals.I sothioureas, [4] one kind of frequently used organocatalyst, initially introduced by Birman [5] and Okamoto, [6] could promote the in situ generation of ammonium enolates from ac arboxylic acid, introducing functionalization to the carboxylic acid throughaMichaellactonization sequence. [7] 1,2-Diaza-1,3-dienes, generatedf rom the corresponding a-halo hydrazones,h ave recently been identified as ar obust and versatile synthetic building blocks with wide applications in the assembly of various five-, six-,a nd seven-membered heterocyclic ring systems. [8] In 2014, the Glorius group reported the first example of NHC-catalyzedf ormal [4+ +3] and [4+ +1] annulationso f1 ,2-diaza-1,3-dienes with enals, providing ah ighly enantioselective access to the chiral dihydrodiazepinones [9] (Scheme 1a). TheX iao group [10] andt he Luog roup [11] achieved the [4+ +3] and [4+ +2] annulationso ft he in situ generated 1,2-diaza-1,3-dienes with 1,3-dipoles and olefins employinga n inorganic base,l eading to the important building blocks of the tetrazepine and tetrahydropyridazine types (Scheme 1b,c ). Inspired by these works,w ee nvisaged that the possible [4+ +2] cycloadditionb etween a-halo hydrazones and arylacetic acids under the cat- COMMUNICATIONS alysis of isothiourea wouldp rovide an efficienta ccess to dihydropyridazinone derivatives.H erein, we report the first example of isothiourea-catalyzed formal [4+ +2] annulation reactions of in situ generated azoalkenesw ith arylacetic acids,c onstructing 4,5-dihydropyridazin-3(2H)-one derivatives in moderate to excellent yields (Scheme 1d). We started our investigation with the reaction between readilya vailable a-chloro N-Boc-hydrazone 1a and phenylacetic acid 2a.W hen the reactionw as performed in DCE at ambient temperature,c ompound...

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An efficient and straightforward method for the production of 5-(3-indolyl)azoles incorporating the privileged structures indoles and azoles via palladium-catalyzed double C-H bond cleavage under mild conditions was disclosed. As expected, this protocol provided an easy method for the synthesis of indole alkaloids pimprinine and WS-30581 A in moderate yields.

Organocatalyzed Formal [4 + 2] Cycloaddition of in situ Generated Azoalkenes with Arylacetic Acids: An Efficient Approach to the Synthesis of 4,5-Dihydropyridazin-3(2H)-ones. -The reaction is suitable for the preparation of various target compounds, inter alia scaffolds of a broad spectrum of pharmaceutical agents. Preliminary studies reveal the possibility of a successful asymmetric version [cf. (IIIa)]. Some derivatizations of racemic derivative (IIIa) are also presented. -(LI, X.; GAI, K.; YUAN, Z.; WU, J.; LIN*, A.; YAO, H.; Adv. Synth. Catal. 357 (2015) 16-17, 3479-3484, http://dx.

Simple and facile methods for the synthesis of deuterium-labeled obeticholic acid and its 2 metabolites, glycine and taurine conjugates of obeticholic acid, are described herein. The 3 deuterated compounds were applicable for use as internal standards in drug development.