Umpolung Synthesis of Selenoesters and Telluroesters via the Photoinduced Coupling of Acylsilanes with Electrophilic Chalcogen Reagents.

A novel synthesis of selenoesters and telluroesters based on the reactions of nucleophilic siloxycarbenes, which were generated by the visible-light-induced isomerization of the corresponding aroyl-, heteroaroyl-, or alkenoylsilanes, with electrophilic chalcogen reagents was developed. The use of appropriate selenides or ditellurides/Lewis acids enabled the coupling at temperatures below ambient temperature with a broad substrate scope and high functional-group tolerance. To the best of our knowledge, this is the first example of a synthetic method for selenoesters and telluroesters involving the combination of an acylanion equivalent and cationic chalcogen synthons.

Photoinduced Intramolecular Cyclization of Acylsilanes Bearing a Boronate Moiety: Construction of a Highly Strained Fused Bicyclo[3.3.0]octane Skeleton.

A reliable strategy for the construction of -fused bicyclo[.3.0] skeletons was explored by utilizing photoinduced cyclization of acylsilanes bearing a boronate.

Generation of (amino)(boryloxy)carbenes from carbamoylboranes and their coupling reaction with aldehydes.

Carbamoylboranes were found to react with various aldehydes under heating conditions to give α-hydroxycarboxamides in good yields. A DFT study supports the mechanism, which involves thermally generated (amino)(boryloxy)carbene intermediates. To our knowledge, this is the first report on the generation of (amino)(boryloxy)carbene intermediates from carbamoylboranes and its application to carbon-carbon bond-forming reactions.

Visible-Light-Induced Generation of Fischer-Type Copper Carbene Complexes from Acylsilanes and Its Application to Catalytic [4 + 1] Cycloaddition with Siloxydienes.

A novel methodology for generation of Fischer-type metal-carbene complexes was developed. Photoirradiation to a mixture of an acylsilane and a cationic copper complex cleanly gave a Fischer-type copper-siloxycarbene complex, which was detected by spectroscopic methods. This carbene complex reacted with siloxydienes in a [4 + 1] cycloaddition manner to give cyclopentene derivatives.

Efficient Generation and Synthetic Applications of Alkyl-Substituted Siloxycarbenes: Suppression of Norrish-Type Fragmentations of Alkanoylsilanes by Triplet Energy Transfer.

Acylsilanes have been known to undergo isomerization to siloxycarbenes under photoirradiation and the thus generated carbenes can be utilized for various synthetic reactions. But this carbene formation is not necessarily efficient with some alkanoylsilanes because Norrish-type fragmentations compete, which limit the synthetic utility of alkanoylsilanes as carbene precursors. In this study, generation of siloxycarbenes from alkanoylsilanes by visible-light-induced energy transfer was examined by using an Ir complex, [Ir{dF(CF )ppy} (dtbpy)]PF , and was successfully applied to the C-C coupling reactions with boronic esters or aldehydes.

Lewis Acid-Assisted Photoinduced Intermolecular Coupling between Acylsilanes and Aldehydes: A Formal Cross Benzoin-Type Condensation.

Intermolecular carbon-carbon bond-forming reaction between readily available acylsilanes and aldehydes was achieved under photoirradiation conditions with assistance of a catalytic amount of Lewis acid. Nucleophilic addition of photochemically generated siloxycarbenes to aldehydes followed by 1,4-silyl migration afforded synthetically useful α-siloxyketones. Electrophilic activation of aldehydes by Lewis acid is highly important to realize this reaction efficiently, otherwise the yield of the desired coupling products were significantly decreased.

Total Synthesis of (±)-Integrifolin.

The total synthesis of (±)-integrifolin has been achieved for the first time through the stereoselective preparation of the bicyclo[5.3.0]decane skeleton based on the tungsten-catalyzed cyclization of acyclic trienynes under photoirradiation conditions.

Total Synthesis of (±)-Englerin A Using An Intermolecular [3+2] Cycloaddition Reaction of Platinum-Containing Carbonyl Ylide.

Total synthesis of (±)-Englerin A has been achieved starting from γ,δ-ynone 5 in 14 steps. The key feature of this synthesis is the highly efficient and stereoselective preparation of 8-oxabicyclo[3.2.

Total Synthesis of Proposed Structure of Yuremamine and All Diastereomers Using [3+2]-Cycloaddition of Platinum-Containing Azomethine Ylide.

Total synthesis of the proposed structure of yuremamine has been achieved for the first time based on the intermolecular [3+2]-cycloaddition reaction of the platinum-containing azomethine ylide. All the possible diastereomers of yuremamine were also synthesized via the common intermediate. Through these syntheses, it was confirmed that the proposed structure of yuremamine and the diastereomers differ from the natural product.

Cobalt-salen complex-catalyzed oxidative generation of alkyl radicals from aldehydes for the preparation of hydroperoxides.

Catalytic generation of alkyl radicals from aldehydes via oxidative deformylation was realized using a cobalt-salen complex with H2O2. The deformylation was thought to proceed through homolytic cleavage of peroxohemiacetal intermediates to provide even primary alkyl radicals under mild conditions. Variously substituted and functionalized hydroperoxides were obtained from corresponding aldehydes in good yield.

Tungsten(0)- and rhenium(I)-catalyzed tandem cyclization of acetylenic dienol silyl ethers based on geminal carbo-functionalization of alkynes.

Tungsten(0)- and rhenium(I)-catalyzed reactions of acetylenic dienol silyl ethers based on the concept of geminal carbo-functionalization of alkynes are reported. Treatment of 3-siloxy-1,3-diene-7-ynes with catalytic amounts of [W(CO)(6)] or [ReCl(CO)(5)] under photoirradiation conditions gives synthetically useful bicyclo[3.3.

Photochemically promoted transition metal-free cross-coupling of acylsilanes with organoboronic esters.

Intermolecular carbon-carbon bond formation between acylsilanes and organoboronic esters was achieved by photoirradiation under almost neutral, transition metal-free conditions. In this reaction, siloxycarbenes generated by photoisomerization of acylsilanes reacted with boronic esters to give the formal B-C bond insertion intermediates, which underwent unique rearrangement to afford the cyclic α-alkoxyboronic esters. Acidic treatment of the resulting crude products under air furnished the cross-coupled ketones in good yields.

Platinum(II)-catalyzed generation and [3+2] cycloaddition reaction of α,β-unsaturated carbene complex intermediates for the preparation of polycyclic compounds.

Pt(II)-catalyzed generation of unsaturated carbene complex intermediates from various propargyl ether derivatives based on electrophilic activation of alkynes was realized. These in situ generated unsaturated carbene complexes undergo [3+2] cycloaddition reaction with various vinyl ethers, leading to efficient formation of indoles, naphthols, and benzofuran fused with a five-membered ring in high yields.

Synthetic studies on and mechanistic insight into [W(CO)5(L)]-catalyzed stereoselective construction of functionalized bicyclo[5.3.0]decane frameworks.

Stereoselective preparation of a variety of synthetically useful functionalized bicyclo[5.3.0]decane derivatives was achieved by tandem cyclization of 3-siloxy-1,3,9-triene-7-yne derivatives based on the electrophilic activation of alkynes catalyzed by [W(CO)(5)(L)].

Enantioselective preparation of 8-oxabicyclo[3.2.1]octane derivatives via asymmetric [3+2]-cycloaddition of platinum-containing carbonyl ylides with vinyl ethers.

A catalytic asymmetric synthesis of 8-oxabicyclo[3.2.1]octane derivatives was achieved through the [3+2]-cycloaddition of the platinum-containing carbonyl ylides generated from acyclic gamma,delta-ynones on treatment with 10 mol % of PtCl(2)-Walphos and AgSbF(6).

Platinum(II)-catalyzed intermolecular [3 + 2] cycloaddition of propadienyl silyl ethers and alkenyl ethers.

A Pt(II)-catalyzed [3 + 2] cycloaddition reaction of silyl propadienyl ethers and alkenyl ethers has been developed as the first example of the utilization of allenes as a three-carbon unit in a transition-metal-catalyzed intermolecular cycloaddition reaction. Pt(II)-containing 1,3-dipole equivalents generated by electrophilic activation of silyl propadienyl ethers using a Pt(II) catalyst reacted with various electron-rich alkenes to give synthetically useful functionalized cyclopentene derivatives in high yield with wide generality.

Theoretical study of the cycloaddition reaction of a tungsten-containing carbonyl ylide.

The [3+2] cycloaddition reaction of a tungsten-containing carbonyl ylide with methyl vinyl ether and the insertion reactions of the nonstabilized carbene complex intermediates produced have been investigated through the use of B3LYP density functional theory. The [3+2] cycloaddition reaction of the tungsten-containing carbonyl ylide has been proven to proceed concertedly, reversibly, and with high endo selectivity. The intermolecular Si-H insertion reactions of the carbene complex intermediates have been proven to be favored over the intramolecular C-H insertion, in good agreement with experimental results.