Synthesis of 1,4-dihydro-benzo[d][1,3]oxazin-2-ones from phthalides via an aminolysis-Hofmann rearrangement protocol

TfOH-Catalyzed Cascade Reaction: Metal-Free Access to 3,3-Disubstituted Phthalides from o-Alkynylbenzoic Acids

A facile new method for the synthesis of 3,3-disubstituted phthalides is reported. A successive reaction process begins with the TfOH-catalyzed cyclization of o-alkynylbenzoic acids followed by an ortho-regioselective electrophilic alkylation of various electron-rich aromatic compounds or alkenes, which has been successfully developed. The corresponding regioselective products of 3-substituted phthalide were obtained in good to high yields.

Convenient synthesis of N-alkyl-3,1-benzoxazin-2-ones from carbamate protected anthranil aldehydes and ketones via one-step alkylation/alkoxy rearrangement

A practical and step-economical protocol was developed to prepare N-alkyl-3,1-benzoxazin-2-one derivatives from anthranil aldehydes and ketones via one-step alkylation/alkoxy rearrangement, where three new chemical bonds and one ring were constructed in a single step. Control studies revealed a stepwise mechanism and that the alkoxy rearrangement was an intermolecular process.

Electrochemical Rearrangement of 3-Hydroxyoxindoles into Benzoxazinones

We report an unexpected rearrangement of 3-hydroxyoxindoles into benzoxazinones using electrochemistry. Our reaction employs mild and environmentally friendly conditions, and the benzoxazinone products are obtained in moderate to excellent yields. Mechanistic experiments suggest that a peroxide intermediate is likely involved.

Carbon dioxide based methodologies for the synthesis of fine chemicals

Rapid environmental changes triggered by the increase in the concentration of heat-absorbing gases such as CO2 in the atmosphere have become a major cause of concern. One of the ways to counter this growing threat will be to efficiently convert atmospheric CO2 into value-added products via the development of efficient transition-metal-catalyzed processes. Conversion of CO2 into bulk products such as CH3OH and methane as well as its incorporation into commercial polyurethane synthesis has been achieved and reviewed extensively. However, the efficient transformation of CO2 into fine chemicals and value-added chemicals has many fold advantages. Recent years have seen a rapid rise in the number of metal-mediated protocols to achieve this goal of converting CO2 into fine chemicals. These are essential developments given the requirement of several commodities and fine chemicals in various industrial processes and the utilization of atmospheric CO2 will help provide a sustainable solution to the current environmental problems. Accordingly, we present here a comprehensive compilation of catalytic processes, involving CO2 as the C1 source for reacting with substrates such as alkanes, alkenes, alkynes, amines, acid chlorides, alcohols, allyl boronates, alkenyl triflates, and many others to provide easy access to a wide variety of useful molecules. Such a technology would certainly prove to be beneficial in solving the problems associated with the environmental accumulation of CO2.

An Entry to Enantioenriched 3,3-Disubstituted Phthalides through Asymmetric Phase-Transfer-Catalyzed γ-Alkylation

A novel asymmetric phase-transfer-catalyzed γ-alkylation of phthalide 3-carboxylic esters has been developed, giving access to 3,3-disubstituted phthalide derivatives, which present a chiral quaternary γ-carbon in good to excellent yields and good enantioselectivities (74–88% ee). The enantiomeric purity could be substantially enhanced to 94–95% ee by recrystallization. Both electron-withdrawing and electron-releasing substituents are well tolerated on the phthalide core as well as on the aromatic moiety of the alkylating agent. This methodology, enabling the introduction of an unfunctionalized group at the phthalide γ-position, fully complements previously reported organocatalytic strategies involving functionalized electrophiles, thus expanding the scope of accessible 3,3-disubstituted products. The high synthetic value of this asymmetric reaction has been proven by the formal synthesis of the naturally occurring alkaloid (+)-(9S,13R)-13-hydroxyisocyclocelabenzine.

Recent advancements in synthetic methodologies of 3-substituted phthalides and their application in the total synthesis of biologically active natural products

We have provided a critical review that focuses on key developments in the area of 3-substituted phthalides and their role in the development of important biologically active natural products. 3-Substituted phthalides are vital molecules owing to their fascinating biological activity. The scope, isolation, and characterization of various naturally occurring racemic and chiral 3-substituted phthalides have been covered. We have put significant emphasis on recently developed research methodologies for the synthesis of racemic and chiral 3-substituted phthalides. These newer approaches are essential for the development of newer and elegant strategies for the synthesis of phthalide-based or similar molecular architecture with broader substrate scope and higher stereoselectivities. Also, we have discussed the application of 3-substituted phthalides as a precursor for the synthesis of natural products and their analogs.

We have provided contextual information on the chemistry of 3-substituted phthalides and their significance in natural product synthesis.

Acid catalysed rearrangement of isobenzofurans to angularly fused phthalides

An acid catalysed, cascade process for the construction of angularly fused polycyclic phthalides from isobenzofurans under transition metal free conditions has been reported. This process is very general for diverse gem-disubstituted isobenzofuran substrates. Control experiments supported the mechanism as the nucleophilic attack of the carboxylate onto the acid activated furan ring for the simultaneous ring closing-ring opening cascade followed by dehydration. This method serves as a greener alternative for the synthesis of angularly fused polycyclic phthalides.

Unprecedented Diastereoselective Arylogous Michael Addition of Unactivated Phthalides

The first highly enantioselective arylogous Michael reaction (AMR) of 3-unsubstituted phthalides has been described. This phase-transfer methodology, which uses catalytic amounts of KOH/18-crown-6 catalyst in mesitylene in the presence of N,O-bis(trimethylsilyl)acetamide (BSA), gives access to a broad range of 3-monosubstituted phthalides with high levels of syn diastereoselectivity and good yields, starting from 3-unsubstituted derivatives and diverse α,β-unsaturated carbonyl compounds. The reaction also applies to unactivated 3-alkyl phthalides to afford 3,3-dialkyl derivatives. A plausible mechanism has been suggested. DFT analysis of possible transition states gives a rationale of the high syn diastereoselectivity observed and its correlation with the solvent's dielectric constant.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

Metal free oxidative coupling of aryl formamides with alcohols for the synthesis of carbamates

A new method under metal free conditions has been developed for the direct transformation of N-aryl formamides to corresponding N-aryl carbamates with alcohols using hypervalent iodine reagents as oxidants. The reaction has been postulated to go through the formation of isocyanate intermediates.

(Tosylimino)phenyl-λ3-iodane as a reagent for the synthesis of methyl carbamates via Hofmann rearrangement of aromatic and aliphatic carboxamides

A new, mild procedure for the Hofmann rearrangement of aromatic and aliphatic carboxamides using (tosylimino)phenyl-λ(3)-iodane, PhINTs, as a reagent is reported. Because of the mild reaction conditions, this method is particularly useful for the Hofmann rearrangement of substituted benzamides, which usually afford complex reaction mixtures with other hypervalent iodine oxidants. The mild reaction conditions and high selectivity in the reaction of carboxamides with PhINTs allow the isolation of the initially formed labile isocyanates or their subsequent conversion to stable carbamates by treatment with alcohols.

Hofmann rearrangement of carboxamides mediated by hypervalent iodine species generated in situ from iodobenzene and oxone: reaction scope and limitations

Alkylcarboxamides can be converted to the respective amines by Hofmann rearrangement using hypervalent iodine species generated in situ from PhI and Oxone in aqueous acetonitrile. On the basis of this reaction, a convenient experimental procedure for the preparation of alkylcarbamates using Oxone as the oxidant in the presence of iodobenzene in methanol has been developed. An efficient method for direct conversion of substituted benzamides to the respective quinone derivatives by treatment with Oxone and iodobenzene in aqueous acetonitrile has also been found.