Development of a flow photochemical process for a π-Lewis acidic metal-catalyzed cyclization/radical addition sequence: in situ-generated 2-benzopyrylium as photoredox catalyst and reactive intermediate.

A flow photochemical reaction system for a π-Lewis acidic metal-catalyzed cyclization/radical addition sequence was developed, which utilizes in situ-generated 2-benzopyrylium intermediates as the photoredox catalyst and electrophilic substrates. The key 2-benzopyrylium intermediates were generated in the flow reaction system through the intramolecular cyclization of ortho-carbonyl alkynylbenzene derivatives by the π-Lewis acidic metal catalyst AgNTf2 and the subsequent proto-demetalation with trifluoroacetic acid. The 2-benzopyrylium intermediates underwent further photoreactions with benzyltrimethylsilane derivatives as the donor molecule in the flow photoreactor to provide 1H-isochromene derivatives in higher yields in most cases than the batch reaction system.

Asymmetric Auto-Tandem Catalysis with Chiral Organosuperbases: Intramolecular Cyclization/Enantioselective Direct Mannich-Type Addition Sequence.

An enantioselective addition reaction of alkynyl esters with imines was developed under asymmetric autotandem catalysis with a chiral Brønsted base. A chiral bis(guanidino)iminophosphorane organosuperbase, which has much higher basicity than that of conventional chiral organic bases, efficiently promoted both the intramolecular cyclization for the construction of a benzofuran ring or a benzothiophene ring and the sequential enantioselective direct Mannich-type reaction of diarylmethane derivatives, affording enantio-enriched diarylalkane derivatives that are otherwise difficult to access.

Consecutive π-Lewis acidic metal-catalysed cyclisation/photochemical radical addition promoted by in situ generated 2-benzopyrylium as the photoredox catalyst.

A π-Lewis acidic metal-catalysed cyclisation/photochemical radical addition sequence was developed, which utilises in situ generated 2-benzopyrylium cation intermediates as photoredox catalysts and electrophilic substrates to form 1H-isochromene derivatives in good yields in most cases. The key 2-benzopyrylium intermediates were generated through the activation of the alkyne moiety of ortho-carbonyl alkynylbenzene derivatives by such π-Lewis acidic metal catalysts as AgNTf2 and Cu(NTf2)2, and the subsequent intramolecular cyclisation and proto-demetalation using trifluoroacetic acid. Further photo-excitation of the 2-benzopyrylium intermediates facilitated single-electron transfer from a benzyltrimethylsilane derivative as a donor molecule to promote the radical addition of arylmethyl radicals to the 2-benzopyrylium intermediates.

Construction of 1,3-Nonadjacent Stereogenic Centers Through Enantioselective Addition of α-Thioacetamides to α-Substituted Vinyl Sulfones Catalyzed by Chiral Strong Brønsted Base.

An enantioselective addition reaction for the construction of 1,3-nonadjacent stereogenic centers is developed by means of a chiral strong Brønsted base catalyst. The chiral sodium ureate catalyst efficiently promoted the reaction of α-thioacetamides as less acidic pronucleophiles with vinyl sulfones having a variety of α-substituents including aryl, alkyl and halo groups, and α-phenylacrylates, accomplishing the construction of various 1,3-nonadjacent stereogenic centers in highly diastereo- and enantioselective manners. This is a rare example of the construction of 1,3-nonadjacent stereogenic centers with less acidic pronucleophiles. In addition, the application of Michael acceptors having various types of α-substituents in a single catalyst system is achieved for the first time, demonstrating the utility of the present catalyst system for the construction of 1,3-nonadjacent stereogenic centers.

Intermolecular exo-selective Diels-Alder reaction catalysed by dual-functional Brønsted acid: conformational restriction of transition states by hydrogen bonds as the key interaction.

An exo-selective Diels-Alder (exo-DA) reaction in which the formed diastereomer is different from that formed in the conventional endo-selective Diels-Alder (endo-DA) reaction was developed, which involves a dual-functional Brønsted acid as a catalyst and not only a dienophile (vinylquinoline) but also an acyclic diene (dienylcarbamate) having a sterically less demanding substituent. Factors necessary for achieving the exo-DA reaction were extracted through an exhaustive computational search of the corresponding transition states, in which the relative orientation of the dienophile and the acyclic diene is firmly defined by hydrogen bonding interactions with a dual-functional Brønsted acid catalyst. It was experimentally verified that the combined use of the dual-functional acid catalyst, such as phosphoric acid, and the conformationally restricted diene (dienylcarbamate), which was realized by the introduction of a substituent at the 2-position of the diene unit, is the key to achieving the exo-DA reaction. A catalytic enantioselective exo-DA reaction was also attempted by using a chiral phosphoric acid catalyst, which gave rise to the corresponding exo-adduct with fairly good enantioselectivity.

Organocatalytic Atroposelective Construction of Axially Chiral Compounds Containing Benzimidazole and Quinoline Rings.

An organocatalytic atroposelective strategy for the construction of axially chiral compounds containing benzimidazole and quinoline rings is described. The enantioselective heteroannulation reaction of 2-alkynylbenzimidazoles with ortho-aminophenylketones proceeded smoothly in the presence of chiral phosphoric acid to provide axially chiral heterobiaryls with good yields and enantioselectivities. This is the first example of the combination of benzimidazole and quinoline rings at the 2- and 3-positions, respectively, into axially chiral heterobiaryls by this new strategy.

Synthesis of Curved Polycyclic Arenes Embedded with Oxepine and Thiepine Using Ring Expansion Strategy.

A tandem oxidative ring expansion of a six- to seven-membered ring was developed to construct a new class of negatively curved polycyclic arenes embedded with oxepine and thiepine, namely, dibenzo[b,f]phenanthro[9,10-d]oxepine (DBPO) and dibenzo[b,f]phenanthro[9,10-d]thiepine (DBPT), respectively. Mechanistic studies disclosed that an unexpected [4 + 2] cycloadduct formed between the alkene moiety of o-biphenyl-linked methylenexanthenes and o-chloranil serves as a radical cation or a dication equivalent that facilitates the FeCl3-mediated tandem ring expansion process.

Silver-Catalyzed para-Selective Sulfenyl Group Transfer Reactions of N-Sulfenylanilides.

Silver-catalyzed reactions of N-sulfenylanilides afforded the corresponding p-sulfenylanilides in good to high yields with good para selectivity. The transformation has a high compatibility of functional groups, such as ester, bromo, and iodo groups. Mechanistic studies indicate that the rearrangement reaction proceeds through intermolecular transfer of the sulfenyl group.

Computational molecular refinement to enhance enantioselectivity by reinforcing hydrogen bonding interactions in major reaction pathway.

Computational analyses have revealed that the distortion of a catalyst and the substrates and their interactions are key to determining the stability of the transition state. Hence, two strategies "distortion strategy" and "interaction strategy" can be proposed for improving enantiomeric excess in enantioselective reactions. The "distortion strategy" is used as a conventional approach that destabilizes the TS (transition state) of the minor pathway. On the other hand, the "interaction strategy" focuses on the stabilization of the TS of the major pathway in which an enhancement of the reaction rate is expected. To realize this strategy, we envisioned the TS stabilization of the major reaction pathway by reinforcing hydrogen bonding and adopted the chiral phosphoric acid-catalysed enantioselective Diels-Alder reaction of 2-vinylquinolines with dienylcarbamates. The intended "interaction strategy" led to remarkable improvements in the enantioselectivity and reaction rate.

Copper-catalyzed [1,3]-nitrogen rearrangement of O-aryl ketoximes via oxidative addition of N-O bond in inverse electron flow.

The [1,3]-nitrogen rearrangement reactions of O-aryl ketoximes were promoted by N-heterocyclic carbene (NHC)-copper catalysts and BF3·OEt2 as an additive, affording ortho-aminophenol derivatives in good yields. The reaction of substrates with electron-withdrawing substituents on the phenol moiety are accelerated by adding silver salt and modifying the substituent at the nitrogen atom. Density functional theory calculations suggest that the rate-determining step of this reaction is the oxidative addition of the N-O bond of the substrate to the copper catalyst. The negative ρ values of the substituent at both the oxime carbon and phenoxy group indicate that the donation of electrons by the oxygen and nitrogen atoms accelerates the oxidative addition.

Synthesis of meta-Aminophenol Derivatives via Cu-Catalyzed [1,3]-Rearrangement-Oxa-Michael Addition Cascade Reactions.

Cu-catalyzed reactions of N-alkoxy-2-methylanilines and alcohols in the presence of catalytic amounts of IPrCuBr and AgSbF6 afforded the corresponding meta-aminophenol derivatives in good to high yields. These reactions proceed via a [1,3]-rearrangement, in which the alkoxy group migrates from the nitrogen atom to the methyl-substituted ortho position, followed by an oxa-Michael reaction of the resulting ortho-quinol imine intermediate.

Scalable Total Synthesis of Leucascandrolide A Macrolactone Using a Chiral Phosphoric Acid/CuX Combined Catalytic System.

A scalable total synthesis of leucascandrolide A macrolactone has been accomplished with a longest linear sequence of 17 steps from readily available feedstocks in 31.2% yield. The key steps in this synthesis are the enantioselective allylation reaction by chiral phosphoric acid (CPA)/CuBr cooperative catalysis and the diastereoselective catalytic crotylation in the presence of CPA with CuCl. These catalytic reactions can be performed on a gram scale to afford the desired products with excellent stereoselectivities.

Enantioselective direct Michael addition of cyanohydrin ether derivatives to enones catalyzed by chiral bis(guanidino)iminophosphorane organosuperbase.

The direct use of cyanohydrin ether derivatives as less acidic pronucleophiles was achieved for the first time in the catalytic enantioselective Michael addition reaction under transition metal free conditions. Chiral bis(guanidino)iminophosphoranes as the higher order organosuperbase facilitated the intended catalytic Michael addition to enones, giving rise to the corresponding products in high yields with moderate to high diastereo- and enantioselectivities in most cases. Further elaboration of the corresponding enantioenriched product was conducted by derivatization into a lactam derivative through hydrolysis followed by cyclo-condensation.

Synthesis of Polysubstituted Naphthofurans and Indenofurans Based on a Regiodivergent Intramolecular Carbometalation Strategy with 2-(2'-Alkynylaryl)-3-iodofurans.

Efficient methods for the synthesis of two types of furan-fused tricyclic compounds were developed based on a regiodivergent intramolecular carbometalation strategy using 2-(2'-alkynylaryl)-3-iodofurans as a common substrate. The iodine-magnesium exchange/copper-mediated 6-endo-anti intramolecular carbometalation sequence followed by nucleophilic substitution or palladium-catalyzed cross-coupling provided 2,3,4,5-tetrasubstituted naphtho[1,2-b]furans. On the other hand, the formal intramolecular 5-exo-anti carbopalladation/cross-coupling sequence afforded 2,3-disubstituted 4-alkylidene-4H-indeno[1,2-b]furans. The present methods provide new access to a wide range of well-organized polysubstituted naphtho[1,2-b]furans and indeno[1,2-b]furans in a positional selective manner that are otherwise difficult to access.

Construction of Alkylidene Fluorene Scaffolds Using Pd-Catalyzed Direct Arene/Alkene Coupling Strategy.

A versatile synthetic method for the construction of alkylidene fluorenes and their heteroarene derivatives has been developed successfully by means of a Pd(II)-catalyzed direct C-H/C-H coupling of o-alkenyl biaryls. Use of the Pd(OAc)2 catalyst under aerobic oxidation conditions gives rise to the corresponding alkylidene fluorenes having various functional groups and diversely fused polycyclic systems. The resulting products can serve as versatile synthetic building blocks for the construction of structurally diverse polycyclic arenes and heteroarenes.

Acquirement of the autonomic nervous system modulation evaluated by heart rate variability in medaka (Oryzias latipes).

Small teleosts have recently been established as models of human diseases. However, measuring heart rate by electrocardiography is highly invasive for small fish and not widely used. The physiological nature and function of vertebrate autonomic nervous system (ANS) modulation of the heart has traditionally been investigated in larvae, transparent but with an immature ANS, or in anesthetized adults, whose ANS activity may possibly be disturbed under anesthesia. Here, we defined the frequency characteristics of heart rate variability (HRV) modulated by the ANS from observations of heart movement in high-speed movie images and changes in ANS regulation under environmental stimulation in unanesthetized adult medaka (Oryzias latipes). The HRV was significantly reduced by atropine (1 mM) in the 0.25-0.65 Hz and by propranolol (100 µM) at 0.65-1.25 Hz range, suggesting that HRV in adult medaka is modulated by both the parasympathetic and sympathetic nervous systems within these frequency ranges. Such modulations of HRV by the ANS in adult medaka were remarkably suppressed under anesthesia and continuous exposure to light suppressed HRV only in the 0.25-0.65 Hz range, indicating parasympathetic withdrawal. Furthermore, pre-hatching embryos did not show HRV and the power of HRV developed as fish grew. These results strongly suggest that ANS modulation of the heart in adult medaka is frequency-dependent phenomenon, and that the impact of long-term environmental stimuli on ANS activities, in addition to development of ANS activities, can be precisely evaluated in medaka using the presented method.

Gold-Catalyzed Intermolecular Alkyne Insertion into the N-S Bond in Sulfenamides.

Gold-catalyzed reactions between sulfenamides and terminal alkynes proceeded via cis-insertion of alkynes into the N-S bond in sulfenamides, affording the corresponding ß-sulfenylenamines in yields up to 90%. Mechanistic studies revealed that the reactions proceeded via nucleophilic attack of the sulfenamide nitrogen atom on the π-activated alkyne, followed by tosylate-assisted intermolecular transfer of the sulfenyl group.

Iridium-Catalyzed Double Asymmetric Hydrogenation of 2,5-Dialkylienecyclopentanones for the Synthesis of Chiral Cyclopentanones.

Herein, we report an efficient iridium-catalyzed double asymmetric hydrogenation of 2,5-dialkylienecyclopentanones, delivering the chiral 2,5-disubstituted cyclopentanones in excellent yields and stereoselectivities. The results of the kinetic experiments and control experiments indicated that the two C═C bonds were hydrogenated in a stepwise manner and the second stereocenter was synergistically controlled by the chiral catalyst and the chirality of monohydrogenated product. The hydrogenated products can be prepared on a gram-scale and are easily derivatized.

Kinetic resolution of racemic tertiary allylic alcohols through SN2' reaction using a chiral bisphosphoric acid/silver(i) salt co-catalyst system.

A highly efficient kinetic resolution (KR) of racemic tertiary allylic alcohols was achieved through an intramolecular allylic substitution reaction using a co-catalyst system composed of chiral bisphosphoric acid and silver carbonate. This reaction afforded enantioenriched diene monoepoxides along with the recovery of tertiary allylic alcohols in a highly enantioselective manner, realizing an extremely high s-factor in most cases. The present method provides a new access to enantioenriched tertiary allylic alcohols, multifunctional compounds that are applicable for further synthetic manipulations.

Formal Umpolung Addition of Phosphites to 2-Azaaryl Ketones under Chiral Brønsted Base Catalysis: Enantioselective Protonation Utilizing [1,2]-Phospha-Brook Rearrangement.

The formal enantioselective umpolung addition of dialkyl phosphites to 2-azaaryl ketones was developed under Brønsted base catalysis. The reaction involves the enantioselective protonation of the transient α-oxygenated (2-azaaryl)methyl anion generated through the 1,2-addition of the anion of dialkyl phosphite to the 2-azaaryl ketone and the subsequent [1,2]-phospha-Brook rearrangement. A chiral bis(guanidino)iminophosphorane organosuperbase efficiently catalyzed the reaction to provide enantio-enriched phosphates in high yields with good to high enantioselectivities. This is a rare example of the catalytic enantioselective protonation of transient carbanions other than enolates, constructing a trisubstituted stereogenic center α to 2-azaarenes.