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The synthesis of pyrimidine‐spirofused indolines from 1,3,5‐triazinanes with 2‐sulfonyliminoindolines has been achieved under catalyst‐ and additive‐free conditions, in which five atoms of 1,3,5‐triazinanes were introduced to the spiro‐annulation products via a (5+1) pathway. Subsequently, this strategy was extended to 3‐aminoindoles and 3‐aminobenzothiophenes, but a different reaction pathway (3+3) was observed. In these cases, three‐atoms of 1,3,5‐triazinanes were incorporated into pyrimidine‐fused indoles/benzothiophenes. These two transformations demonstrate the potential and versatility of 1,3,5‐triazinanes to construct nitrogen‐heterocycles. [ABSTRACT FROM AUTHOR]

Carbenes are pivotal reactive intermediates for accessing a wide range of complex molecules, which are frequently used in chemical synthesis and medicinal advancement. We have developed a convenient approach to fluorenes from α‐biaryldiazoacetates via low‐energy blue light‐induced photochemical generation of a carbene intermediate, where the reaction took place at room temperature without any catalysts, bases, or oxidants in acetonitrile. The present catalyst‐free and operationally simple approach enables highly efficient annulation of α‐biaryldiazoacetates under mild reaction conditions. [ABSTRACT FROM AUTHOR]

The synthesis of 4‐(trifluoromethyl)‐2,3‐dihydrothiazoles from α‐enolic dithioesters and imidoyl sulfoxonium ylides has been achieved under thermal conditions. This transformation is catalyst‐free, additive‐free, and operationally simple, and it proceeds via a formal insertion of alkenyl S−H generated in situ from dithioesters into ylides followed by an intramolecular annulation. This approach further expands the synthetic application of two versatile sulfur‐containing building blocks of fluorinated imidoyl sulfoxonium ylides and α‐enolic dithioesters. [ABSTRACT FROM AUTHOR]

A formal (3+2) annulation reaction between isatin-derived N -tosylhydrazones and o -(trimethylsilyl)aryl triflates allows facile synthesis of spiro[indazole-3,3′-indolin]-2′-ones in high to excellent yields. Furthermore, indazolo[2,3- c ]quinazolin-6(5 H)-ones could be accessed from the same starting materials in one-pot fashion via an annulation/rearrangement pathway. [ABSTRACT FROM AUTHOR]

An efficient annulation reaction of aurone-derived α,β-unsaturated imines and activated terminal alkynes mediated by triethylamine is described, which enables the facile synthesis of 1,4-dihydrobenzofuro[3,2-b]pyridines in high yields. When the nucleophile of triethylamine was replaced with triphenylphosphine, another class of 1,4-dihydrobenzofuro[3,2-b]pyridines tethered with an additional acrylate motif were obtained instead. These two types of 1,4-dihydrobenzofuro[3,2-b]pyridines could be aromatized in the presence of DBU to afford benzofuro[3,2-b]pyridines, which could also be accessed via a one-pot procedure. [ABSTRACT FROM AUTHOR]

The synthesis of hydrobenzoimidazoles from para‐quinamines and 1,3,5‐triazinanes was achieved via a formal [3+2] annulation reaction in the presence of In(OTf)3 as the catalyst. Further studies demonstrated that the synthesis of hydrobenzooxazoles could also be accomplished via the same strategy from para‐quinols and 1,3,5‐triazinanes. [ABSTRACT FROM AUTHOR]

A [4+2] annulation reaction of 1,3,5‐triazinanes and aurone‐derived α,β‐unsaturated imines has been developed, which enables the synthesis of 1,2,3,4‐tetrahydrobenzofuro[3,2‐d]pyrimidines under thermal conditions in high yields. This protocol is catalyst‐free and additive‐free. [ABSTRACT FROM AUTHOR]

Cyclopianes are novel diterpenes featuring a highly strained 6/5/5/5 tetracyclic core embedded with 6–8 consecutive stereocenters. The concise total syntheses of (−)‐conidiogenone B, (−)‐conidiogenone, and (−)‐conidiogenol have been accomplished in 14–17 steps. The present work features a HAT‐mediated alkene–nitrile cyclization to access the cis‐biquinane, a Nicholas/Pauson–Khand reaction to construct the linear triquinane, and a Danheiser annulation to afford the congested angular triquinane skeleton. [ABSTRACT FROM AUTHOR]

The synthesis of pyridothiazines was achieved using pyridinium 1,4-zwitterionic thiolates and α-functionalized bromoalkanes via a formal [5+1] pathway. Further studies demonstrated that the synthesis of indolizines could be accomplished via a stepwise [(5+1)−1] pathway with unstable pyridothiazines as the transient intermediates from the same starting materials. The net transformation involves a sequence of annulation, oxidation and ring-contraction/desulfuration. [ABSTRACT FROM AUTHOR]

We have developed a one-pot synthesis of benzo[b]fluorenones via a cobalt-catalyzed [3+2] annulation of oxabicyclic alkenes followed by a ring-opening/dehydration sequence in good to excellent yields. With the use of 2-(1-methylhydrazinyl)pyridine (MHP), first explored by our group as the bidentate directing group in C–H functionalization of benzoic hydrazides, the new reaction sequence proceeded smoothly and tolerated a wide range of functional groups, featuring facile scalability. Notably, oxygen served as the green oxidant in the reaction system. Careful tuning of the reaction parameters assured the direct synthesis of benzo[b]fluorenones through aromatization of the dihydroepoxybenzofluorenone intermediate. [ABSTRACT FROM AUTHOR]

Newstereocontrolled total syntheses of (±)-fawcettimine,(±)-lycoflexine, and (±)-lycoflexine N-oxidehave been accomplished. The highlights include a one-pot annulationto construct the enedione and a microwave-promoted Diels–Alderreaction. [ABSTRACT FROM AUTHOR]

The synthesis of pyrazolotetrazepin-7-ones from 1,3,5-triazinanes with N,N′-cyclic azomethine imines was achieved via a formal (5 + 2) pathway under thermal conditions. The annulation reaction is catalyst-free and additive-free. [Display omitted] • The synthesis of pyrazolotetrazepin-7-ones from 1,3,5-triazinanes with N,N′-cyclic azomethine imines was achieved via a formal (5 + 2) pathway under thermal conditions, which is catalyst-free and additive-free. • Different from traditional reaction modes of 1,3,5-triazinane in the literature, five atoms of 1,3,5-triazinane were involved in this annulation reaction, which is more fascinating and useful. • N,N'-cyclic azomethine imines were used as a two-atom synthon via releasing benzaldehyde, which is the first case in the literature. [ABSTRACT FROM AUTHOR]

A cascade consisting of a Wittig reaction, a Staudinger reaction between propargyl azide and triphenylphosphine followed by an aza-Wittig reaction with subsequent 6π-3-azatriene electrocyclization and 1,3-H shift furnishes polysubstituted pyridines. [ABSTRACT FROM AUTHOR]