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Tyrosinase is a copper‐containing enzyme involved in the biosynthesis of melanin pigment. While the excess production of melanin causes hyperpigmentation of human skin, hypopigmentation results in medical conditions like vitiligo. Tyrosinase inhibitors could be used as efficient skin whitening agents and tyrosinase agonists could be used for enhanced melanin synthesis and skin protection from UV exposure. Among a wide range of tyrosinase‐regulating compounds, natural and synthetic derivatives of furochromenones, such as 8‐methoxypsoralen (8‐MOP), are known to both activate and inhibit tyrosinase. We recently reported a synthetic approach to generate a variety of dihydrofuro[3,2‐c]chromenones and furo[3,2‐c]chromenones in a metal‐free condition. In the present study, we investigated these compounds for their potential as antagonists or agonists of tyrosinase. Using fungal tyrosinase‐based in vitro biochemical assay, we obtained one compound (3k) which could inhibit tyrosinase activity, and the other compound (4f) that stimulated tyrosinase activity. The kinetic studies revealed that compound 3k caused 'mixed' type tyrosinase inhibition and 4f stimulated the catalytic efficiency. Studying the mechanisms of these compounds may provide a basis for the development of new effective tyrosinase inhibitors or activators. [ABSTRACT FROM AUTHOR]

Herein, DFT studies corroborating experimental results revealed that the shortest intramolecular hydrogen bonding distance of cis/trans‐oxaphosphetane (OPA) oxygen with the CH‐hydrogen of a triphenylphosphine phenyl ring provides good evidence for the attained olefin Z/E‐selectivity in Wittig olefination of the studied examples. 2‐Nitrobenzaldehyde, 3‐nitrobenzaldehyde, 2‐nitro‐3‐bromobenzaldehyde, 2‐nitro‐5‐bromobenzaldehyde and 2‐nitro‐5‐arylbenzaldehydes provided Z‐nitrostilbenes with (2‐chloro‐4‐hydroxy‐3‐methoxy‐5‐(methoxycarbonyl)benzyl) triphenylphosphonium chloride as the major products. However, 4‐nitrobenzaldehyde and 2‐nitro‐6‐bromobenzaldehydes furnished E‐nitrostilbenes as the major products in high yields. Furthermore, the DFT computed intramolecular CH1/CH2‐hydrogen bond distances with Cl/NO2 of selected stilbene derivatives were in good agreement with intramolecular hydrogen bond distances measured from single‐crystal X‐ray diffraction measurements. [ABSTRACT FROM AUTHOR]

A mild and transition‐metal‐free one‐pot strategy is established to prepare polysubstituted naphthalene and phenanthrene derivatives from methyl enol ethers (MEE) with alkynes. Significantly, this protocol is promoted by boron trifluoride diethyl etherate (BF3⋅Et2O) at room temperature. A wide variety of diversely functionalized naphthalene and phenanthrene derivatives were obtained in good to excellent yields. A plausible mechanism involving a spiro quinonoid intermediate is proposed. Due to fluorescent nature of naphthalene, selected compounds were screened for the solvatochromism study. Notably, positive solvatochromism effect was observed in the case of nitro‐substituted naphthalene derivative (3 h) with respect to different polarity of solvents. [ABSTRACT FROM AUTHOR]

Alkyl enol ethers (AEE) are versatile synthetic intermediates with a unique reactivity pattern. This review article summarizes the synthesis of AEE as well as its reactivity and how enol ether undergoes intermolecular reactions for various bond formation, leading to the construction of several useful organic molecules. The synthetic applications of alkyl enol ethers towards intermolecular bond‐forming reactions include metal‐catalyzed reactions, cycloaddition and heterocycle formation as well as rwactions in the field of natural products synthesis. The achievement of these impressive transformations prove the countless synthetic potential of AEE. The main objective of this review is to bring attentiveness among synthetic chemists to show how AEE extensively can be used to react with both electrophiles as well as nucleophiles, thereby behaving as an ambiphilic reactant. We trust that the unique reactivity pattern of alkyl enol ethers and the fundamental mechanistic idea can attract chemists in AEE chemistry. Exclusively, intermolecular reactions of AEE with other functionalized moieties have not been reviewed to the best of our knowledge. [ABSTRACT FROM AUTHOR]

The base-mediated formation of a bridgehead double bond in a bicyclo[2.2.1]heptane system (anit-Bredt molecules) is described. The synthesis of exocyclic norbornyl enones by Wittig reaction of α-diketones is reported. These enones and their Michael adducts are used as substrates for the generation of transient bridgehead enones and their trapping with MeOH and H2O. Bridgehead alcohols are easily synthesized from norbornyl enones and are exploited for the diversity oriented synthesis of frameworks of natural and unnatural products. [ABSTRACT FROM AUTHOR]

A diastereoselective zinc-mediated propargylation of non-enolizable norbornyl α-diketones and an efficient AgI-catalyzed cycloisomerization of the resulting α-keto homopropargyl alcohols with terminal alkynes leading to spirocyclic dihydrofurans have been reported. The dihydrofurans obtained were subjected to hydrogenation to afford spiro tetrahydrofuran derivatives in nearly quantitative yields (98-99 %). Eventually, the prepared α-spiro tetrahydrofuran norbornyl monoketones were utilized as precursors for acid-mediated Grob-type fragmentation reactions and converted into 1-oxaspiro[4.5]decan-6-one derivatives by treatment with p-toluenesulfonic acid. [ABSTRACT FROM AUTHOR]

An abstract of the article "Aromaticity Driven 1,6-Conjugate Addition of Amines and Phenols to Cyclohexadienone Derivative" by Kaki Raveendra Babu and colleagues is presented.

The title isomerizations of the substrates having disubstitution at benzylic position give different products depending on the nature of the substitution. [ABSTRACT FROM AUTHOR]

This unusual dimerization of substrates (I) proceeds via a dehydrohalogenation/1,6-conjugate addition/aromatization sequence. [ABSTRACT FROM AUTHOR]

The efficient and versatile synthesis allows for the preparation of compounds bearing one or two 3-substituted butenolide moieties. [ABSTRACT FROM AUTHOR]

Various spirocyclic dihydrofuran structures are prepared in a diastereoselective manner following the sequence shown for (IV) and (VII). [ABSTRACT FROM AUTHOR]

The article presents chemical equations of the article "Synthesis of the Tetrahydrofuran Unit of Varitriol and ᵞ-Butyrolactones from 5-Oxabicyclo[2.1.1]hexane Derivative via Oxidative Cleavage Reactions" by F. A. Khan and others, published in the periodical "Tetrahedron Letters" in 2014.

A stereoselective Grob-fragmentation of 5-oxabiocyclo[2.1.1]hexane derivatives is developed allowing the synthesis of annulated 2,2,5-trisubstituted tetrahydrofurans. [ABSTRACT FROM AUTHOR]