About the stereoelectronics of the intramolecular addition of allylsilanes to aldehydes

(Z)-omega-Trimethylsilyl-(omega-2)-alken-1-ols are readily accessible by consecutive superbase metalation and silylation of (omega-1)-alken-1-ols. These versatile intermediates may be oxidized to give the corresponding (Z)-omega-trimethylsilyl-(omega-2)-alkenals which, in the presence of trifluoroacetic acid, can be converted into 2-vinylcycloalkanols such as 2-vinylcyclohexanol (2), isopulegol (4), and bis(2-vinylcyclobutyl) ether (8). The stereochemical outcome of these cyclization reactions suggests the interference of a novel electrodynamic effect.     

Organocatalyst-mediated enantioselective intramolecular Michael addition of aldehydes to vinyl sulfones

Chiral amines with a hydrogen bond donor promote the intramolecular conjugate addition of aldehydes to vinyl sulfones. Chiral cyclic sulfone-aldehydes are obtained in good yields with an ee of up to 82%.     

Antibody-catalyzed asymmetric intramolecular Michael addition of aldehydes and ketones to yield the disfavored cis-product

The development of new catalytic asymmetric reactions continues to be a major goal in organic chemistry. Here we report a novel antibody-catalyzed intramolecular Michael addition of aldehydes and ketones to enones. The reaction is enantioselective and diastereoselective with a high ee value and cis/trans ratio. This is the first example of asymmetric intramolecular Michael addition of ketones. Antibody 38C2 is the only catalyst to date capable of generating this selectivity in Michael addition products.     

Synthesis of lactones by intramolecular addition of alkoxythiocarbonyl free radicals to acetylenes

Lactones are obtained by treating dithiocarbonates of homopropargylic or homoallylic alcohols with n-Bu³SnH-Et₃B.     

Enthalpies of addition of radicals to aldehydes, ketones, acids and esters

Enthalpies of the addition of radicals HO^•, HO₂ ^•, CH₃ ^•, CH₃O^•, CH₃O₂ ^• to the C=0 bond of model aldehydes, ketones, acids and esters have been calculated by thermodynamic and quantum chemical methods. It has been shown that the exothermic effect of these reactions decreases in the row HO^•>CH₃O^•>CH₃ ^•>HOO^•>CH₃OO^•.     

On the stereochemical course of the addition of allylsilanes to aldehydes

Model compounds 3 and 5 have been studied to determine the orientation of the reacting double bonds in the transition state of the allylmetal–aldehyde addition. These models were designed to remove any intrinsic steric bias for the formation of the bicyclic products that would obfuscate a stereoelectronic contribution to the transition states. Model system 3 revealed a modest preference for the synclinal transition state, albeit in very low yields. Model system 5 underwent selective and largely Lewis acid independent cyclization primarily via a synclinal transition state. The high proximal selectivity observed in these cyclizations likely reflects the selectivity of an unhindered allylmetal–aldehyde addition for the synclinal transition state and results from a stereoelectronic preference, not an intrinsic steric bias, for the synclinal arrangement of double bonds.     

Intramolecular addition of carbon radicals to aldehydes: synthesis of enantiopure tetrahydrofuran-3-ols

A simple and efficient substrate-controlled asymmetric synthesis of enantiopure tetrahydrofuran-3-ols by a 5-exo-trig radical cyclization is described. This cyclization occurs when a δ-carbon radical adds intramolecularly to the carbonyl group of an aldehyde. The δ-carbon radicals can be efficiently produced from the tin hydride mediated deselenenylation of 5-phenylseleno-3-oxapentanals, which were easily prepared starting from commercially available enantiopure epoxides or chlorohydrins.     

Cationic palladium complex catalyzed highly enantioselective intramolecular addition of arylboronic acids to ketones. A convenient synthesis of optically active cycloalkanols

An efficient and convenient synthesis of optically active cycloalkanols by utilizing the chiral cationic palladium complex as the catalyst was achieved in mild conditions with high yield and high enantioselectivity.     

Radicals masquerading as electrophiles: a computational study of the intramolecular addition reactions of acyl radicals to imines

Ab initio calculations using 6-311G**, cc-pVDZ, and aug-cc-pVDZ, with (MP2, QCISD, CCSD(T)) and without (UHF) electron correlation, and density functional methods (BHandHLYP and B3LYP) predict that cyclization of the 5-aza-5-hexenoyl and (E)-6-aza-5-hexenoyl radicals proceed to afford the 5-exo products. At the CCSD(T)/cc-pVDZ//BHandHLYP/cc-pVDZ level of theory, energy barriers (deltaE(double dagger)) of 36.1 and 47.0 kJ mol(-1) were calculated for the 5-exo and 6-endo pathways for the cyclization of the 5-aza-5-hexenoyl radical. On the other hand, at the same level of theory, deltaE(double dagger) of 38.9 and 45.4 kJ mol(-1) were obtained for the 5-exo and 6-endo cyclization modes of (E)-6-aza-5-hexenoyl radical, with exothermicities of about 27 and 110 kJ mol(-1) calculated for the exo and endo modes, respectively. Under suitable experimental conditions, the 6-endo cyclization product is likely to dominate. Analysis of the molecular orbitals involved in these ring-closure reactions indicate that both reactions at nitrogen are assisted by dual orbital interactions involving simultaneous SOMO-pi* and LP-pi* overlap in the transitions states. Interestingly, the (Z)-6-aza-5-hexenoyl radical, that cannot benefit from these dual orbital effects is predicted to ring-close exclusively in the 5-exo fashion.     

On the question of heavy-atom blocking of intramolecular vibrational energy transfer

The possibility that a heavy atom can block internal energy transfer in excited species has been further investigated by chemical activation study of 4-(trimethyl lead)-2-butyl and 5-(trimethyl tin)-2-pentyl radicals. These radicals were prepared and excited by the reaction of H atoms with the corresponding 1-olefins. Energy randomization was found to occur on a subpicosecond time scale in all the radicals studied.     

Diastereoselective addition of γ-alkylthio-allylboronates to aldehydes

The Z- and E-γ-alkylthio-allylboronates $\text{5}$ and $\text{10}$ were found to add aldehydes forming diastereoselectively the adducts $\text{7}$ and $\text{6}$ respectively in high yield.     

Palladium-catalyzed addition of arylboronic acids to aldehydes

[reaction: see text] Arylboronic acids react with aldehydes in the presence of a base and a catalytic amount of a palladium(0) complex with chloroform, affording the corresponding secondary alcohols in good yields. General palladium complexes have no catalytic activity without chloroform. Chloroform is essential for this reaction, and palladium complex that was prepared from Pd(PPh3)4 with CHCl3 showed good catalytic acitivity as well.     

The asymmetric addition of phenylacetylene to aldehydes

Enantioselective formation of C-C bonds is an area of intense research.Among them, the asymmetric addition of alkynyl reagents to aldehydes is very useful for the synthesis of chiral secondary propargyl alcohols, which are very important building blocks for many chiral organic compounds, and the acetylene and hydroxyl founctional group of propargyl alcohol can be easily transfered into many other structures.1Recently, many significant chiral ligands have been disclosed.2 Here, we report our r…     

Syn-selective addition of enol borates to aldehydes

Both the Z- and the E-enolborate 4 and 6 add to aldehydes in a stereoconvergent reaction to give β-hydroxyketones with a $\text{syn}$/$\text{anti}$-ratio of ≧ 9 : 1.     

Acyclic stereocontrol in the addition of γ-alkylthio-allylboronates to aldehydes

The Z-isomer 10 of the γ-alkylthio-allylboronates adds to aldehydes giving the syn diastereomer 4 of the product homoallyl-alcohol. The E-isomer 12 leads in turn to the anti-diastereomer 5 with a high degree of acyclic stereocontrol. Kinetic diastereoselection can be applied to obtain the anti-diastereomer 5 even when using E/Z-mixtures of the γ-alkylthio-allylboronates.     

The photochemical addition of aldehydes to vinylsilanes

Conclusions The photochemical reaction of aldehydes of various structures with vinyl and allylsilanes have been investigated. A number of features of this reaction has been established and a convenient method for the synthesis of -silicon-containing ketones, including ketones containing a readily saponifiable alkoxy group on the silicon atom, have been found.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1464–1466, August, 1966.     

Mandelamide-zinc-catalyzed enantioselective alkyne addition to heteroaromatic aldehydes

The (S,S)-mandelamide III catalyzes the additions of both aryl- and alkylalkynylzinc reagents to heteroaromatic aldehydes with good yields and enantioselectivities up to 92%. This catalyst is easily prepared in a one-step procedure, and both enantiomers are available. Unlike most other described methods, using this catalyst does not require the addition of Ti(O(i)Pr)4.     

Catalytic asymmetric intramolecular alpha-alkylation of aldehydes

The development of a general catalytic asymmetric aldehyde alpha-alkylation reaction constitutes a major challenge in organic synthesis. Here, we report the first and successful approach toward its solution: (S)-alpha-methyl proline catalyzes the intramolecular alkylation of various halo aldehydes to the corresponding formyl cyclopentanes, -cyclopropanes, or -pyrrolidines in excellent yields and enantioselectivities. Most remarkably, racemization, aldolization, or catalyst alkylation do not occur to any significant extend, further illustrating the power, mildness, and profound selectivity of enamine catalysis.