Highly regio- and syn-diastereoselective synthesis of 4-hydroxy-1,2-alkadienylcarbamates from α-titanatedl 2-alkynylcarbamates and aldehydes1,2

$\text{N}$,$\text{N-}$Diisopropyl 2-alkynyl carbamates 9 are deprotonated by $\text{n}$-butyllithium to form lithium compounds 10. After exchange of the cation, titanium reagents 13 add highly diastereoselective to aldehydes with formation of the title compounds 14. In contrast to metallated 2-alkynyl ethers, the reagents 10 and 13 exhibit high γ-regioselectivity in carbonyl addition reactions, due to the chelating carbamoyl group. The $\text{syn}$-configuration of 14 was deduced from the crystal structure of the urethane derivative 21.     

Structural effects on valence tautomerism : VII. An NMR and molecular mechanics study of the steric effects of t-butyl substituents on the cycloheptatriene-norcaradiene equilibrium of 7-cyano-7-m

7-Cyano-7-methylcycloheptatrienes containing one t-butyl group on the 1-position ($\text{2}$) or two t-butyl groups on the 1- and 3-, 1- and 4-, or 1- and 5-positions ($\text{3}$, $\text{4}$, or $\text{5}$, respectively) were synthesized and their cyclo- heptatriene (CHT)-norcaradiene (NCD) equilibria measured by variable-temperature ¹H NMR for CS₂-CD₂Cl₂ solutions. The ¹H NMR chemical shifts of the 7-methyl group indicate that these compounds are composed of essentially one CHT and one NCD tautomer with an endo geometry of the methyl group. The introduction of a t-butyl group at the 1-position of 7-cyano-7-methylcycloheptatriene ($\text{1}$) markedly shifts the equilibrium to the NCD side and the addition of the second t-butyl group further favors the NCD form, with the NCD populations for $\text{2}$, $\text{3}$, $\text{4}$, and $\text{5}$ at 25 °C 70.9, 96.5, 92.3, and 99.3%, respectively. An application of molecular mechanics (MMPI) calculations to various t-butylated CHT-NCD systems suggests that the t-butyl groups sterically destabilize the CHT form more than the NCD form, bringing about increased NCD populations.     

The effect of the solvent upon the rates and mechanisms of organometallic reactions: VI. The complexation of dibenzylmercury in solutions studied by PMR spectroscopy

The concentration and temperature dependence of J(¹¹⁹HgC¹H) values for solutions of dibenzylmercury in various solvents show dearly that if the solvent is of the monodentate electron-donating type $\text{1}\text{1}$ complexes are formed predominantly, the $\text{1}\text{2}$ complexes existing only at very low temperatures. The results suggest that the $\text{1}\text{1}$ complexes are very weak and have planar T-shaped structures, whereas the $\text{1}\text{2}$ complexes are probably tetragonal pyramids. In complexes of the former type the relative content of s-electrons in the HgCH site is higher than in the $\text{1}\text{2}$ complexes.     

Vinylogous urethanes in alkaloid synthesis: formal syntheses of Elaeocarpus alkaloids

The substituted dehydroindolizidine $\text{8}$ has been prepared from the exocyclic vinylogous urethane $\text{7}$ via an acylative ring closure. The specific formation of the enolate required for further elaboration to Elaeocarpus alkaloid precursors has been achieved by making use of the vinylogous amide $\text{12}$.     

The crystal and molecular structure of μ-μ-dichlorobis(hexafluorobut-2-enyl)-bis(cycloocta-1,5-dienyl)diiridium(III).

The title compound is isolated from reaction of hexafluorobut-2-yne with μ-μ-Dichlorobis(cycloocta-1,5-diene)diiridium(I) at 90°C. Crystals of the complex, solvated with deuterobenzene, are monoclinic, space group $\text{P}$2₁/$\text{n}$ with $\text{a}$ = 10.97 $\text{+}$ 0.02, $\text{b}$ = 17.96 $\text{+}$ 0.03, $\text{c}$ = 11.63 $\text{+}$ 0.02 », β = 127.4 $\text{+}$ 0.60°. The acetylene has abstracted a hydrogen atom forming a σ-bonded $\text{cis}$-vinylic group and the original cyclooctadiene, having lost a proton, is coordinated as the cycloocta-1,5-dienyl ligand. Mean bond lengths are IrCl 2.467, IrC (allylic) 2.17, IC (olefinic) 2.36 and IrC (vinylic) 2.09 ».     

On the mode of incorporation of leucine samples labelled at positions 5 and 2 with 3H and 14C into the isoprenylated tryptophan derivative echinuline from aspergillusamstelodami

Feeding experiments with (4$\text{S}$) [5-³H;5-¹⁴C]$\text{L}$-leucine ($\text{1a}$) and with the (4$\text{S}$) [5-³H;2-¹⁴C]-isomer ($\text{1b}$) show that incorporation into the isoprenylated tryptophan derivative echinuline ($\text{3}$), produced by $\text{Aspergillus}$$\text{amstelodami}$, involves, to a large extent, loss of the fragment enbodying the carbon atom at position 2 of the fed amino acid.     

A novel ring substitution reaction in a cyclopentadienylruthenium phosphine complex

The reaction between hexafluoroacetone and Ru(PPh₃)₂(π-C₅H₅)[σ-C₂(CO₂Me)₂H] affords a $\text{1}\text{1}$ adduct, containing a coordinated ester group and an intramolecular hydrogen bond; formal insertion of (CF₃)₂CO into a CH bond of the cyclopentadienyl group has also occurred.     

Quinone-imides : regiospecificity of nucleophilic attack on n-alkanesulphonyl-n'-alkanoyl 14-benzoquinone-imines.

Substrates such as ($\text{2}$) undergo regiospecific attack by azide and thiocyanate ions at the terminus of the CC-CN-CO system. In the case of addition of azide, this is proved by the detailed analysis of the ¹H and ¹³C NMR spectra of the products ($\text{11}$) derived from the quinone-imides ($\text{8}$). The structure of the products obtained by the addition of thiocyanate to the quinone-imides and ($\text{tilde10}$)($\text{tilde20}$) is proved by their facile cyclisation to the 2-aminobenzothiazoles ($\text{18}$) and ($\text{21}$) respectively.     

Syntheses and stereochemistry of 4-hydroxy tetrahydroisoquinolines in the 1-benzyl and 1-phenethyl series. Efficient routes to isopavines and homoisopavines

The title compounds have been prepared in high yield $\text{via}$ cyclisation of urethane acetals.     

The conformation of 4-t-butylcycloheptanone

The 400 MHz ¹H NMR spectra of two deuterated derivatives of 4-t-butylcycloheptanone ($\text{2}$ and $\text{3}$) provided ²J_HH values for the α-methylene protons on each side of the carbonyl group. The interpretation of their magnitude shows clearly that the carbonyl group is located at position 1 of the twist-chair conformation while the t-butyl group is located at position 4e.     

An alternative formation of tricarbonylcyclohexadienylium iron salts by acid-catalysed decarbonylation

The action of concentrated sulphuric acid on ($\text{1}$, R = H or CO₂Me, R′ = H) generates the cation ($\text{2}$, R = H or CO₂Me, R′ = H); the stereoisomer ($\text{5}$, R = H, R′ = H) is unaffected. This is an alternative procedure of some utility for the preparation of some cation salts, notably of ($\text{2}$, R = CO₂Me, R′ = H).     

Biosynthesis of psilotin from [2′,3′-13C2,1′-14C,4-3H]phenylalanine studied with 13C-NMR

The 6-phenyl-dihydro-α-pyrone moiety of psilotin is formed from [2′,3′-¹³C₂,1′-¹⁴C,-4-³H]phenylalanine in the plant $\text{Psilotum}$$\text{nudum}$ with retention of all the isotopes.     

Through-space hydrogen-fluorine and carbon-fluorine spin-spin coupling in 5-fluoro-3,3-dimetryl-1,2,3,4-tetrahydrophenanthrene

The ¹R and ¹³C NMR spectra of the title compound ($\text{1}$) reveal through-space couplings between the fluorine and the C-4 methylene group ¹H and ¹³C), as well as coupling between the fluorine and the C-3 methine carbon and the C-2 methylene carbon.     

Versatilité de la réactivité de l' acétylènedicarbaldéhyde et d'aldéhydes α-acétyléniques à l'égard des diènes conjugués cycliques et hétérocycliques en milieu acide.

Formic solutions of ADCA react with cyclic and heterocyclic conjugated dienes affording the Diels-Alder $\text{1}$ or pseudo-Michael $\text{2}$ adducts depending on the nature of the diene. Generalisation to RCCCHO and furan shows a similar behaviour (RCO₂,Et, H) and a third possible pathway (electr. subst. of CO on α of furan,RAr, Alk); mechanisms are discussed.     

Stéréosélectiveté de la condensation aldolique. Réaction du benzaldéhyde et d'énolates carbéniates magnésiens α-chlorés

Alkyl chloracetates III (R′ = H) and phenylchloracetates III (R′ = Ph) condense with PhCHO in the presence of (i-Pr)₂NMgBr giving alkyl-2-chloro-3-hydroxy-3-phenyl propionates (RS, RS) (I) and (RS, SR) (II) in equal ratio ($\text{1}\text{1}$) for III (R′ = H) and in the ratio $\text{65}\text{35}$ for III (R′ = Ph) irrespective of the group R. When the same reaction is performed with alkyl chloropropionates III (R′ = CH₃) the isomer ratio is dependent upon the group R. These results are interpreted by considering a planar (R′ = H or Ph) or pyramidal (R′ = CH₃) geometry of the intermediate enolate-carbeniate.     

The Mannich reaction of 9-acetyl- and 9,10-dihydro-9-acetylanthracene. Reduction of the Mannich bases, and stereochemistry of the 9,10-dihydro compound

The Mannich derivatives ($\text{2}$ and $\text{5}$) of 9-acetyl-9,10-dihydroanthracene ($\text{4}$) with amines of different sizes were prepared for study of their biological effects. It was found that formation of the normal Mannich product in acetic acid was accompanied by formation of a secondary Mannich product containing a methylidene group ($\text{3}$ and $\text{6}$). Reduction of compounds $\text{5}$ with NaBH₄ gave aminoalcohols ($\text{10}$), and amino-olefins ($\text{11}$) were prepared from these by elimination. The catalytic reduction of compounds $\text{2}$ on Pd/C, Raney Ni and Adams catalysts was studied under acidic and basic conditions. In acidic media on Pd/C, the 9,10-dihydro compounds ($\text{5}$) were formed; under basic conditions, on all three catalysts the hydrogenation led to deamination. However, for “steric hindrance” reasons the keto group was not reduced in any of the cases. In compounds $\text{5}$, the literature data and the H-NMR spectra indicate that the orientation of the 9-substituent is pseudoaxial     

Reaction of 5,5-diphenyl-2-thiohydantoin with 1,2-dibromoethane.crystal and molecular structures of 2,3-dihydro-6,6-diphenylimi-dazo-[2,1-b]-thiazol-5(6h)-one and 2,3-dihydro-5,5-diphenylimi-dazo-[2,-1-b]-thiazol-6(5h)-one and their reactivity

The crystal and molecular structures of the title isomeric compounds $\text{1}$ and $\text{2}$, obtained by intramolecular N,S--dialkylation of 5,5-diphenyl-2-thiohydantoin with 1,2-dibro-moethane, have been determined from X-ray diffractometer data. 2,3-Dihydro-6,6-diphenylimidazo-[2,1-b]-thiazol-5(6H)-one $\text{1}$ crystallizes in space group P2₁2₁2₁ with a=11.376(3), b=12,255(5), c=8.434(3) Å and Z=4. Crystals of $\text{2}$, containing one molecule of benzene, are monoclinic,space group P2₁/c with a=11.539(6), b=10.242(3), c=16.353(5) Å, β=95.45(5)° and Z=4. In both cases a planar geometry of the two fused five-membered heterocyclic rings was found. The selected bond lengths in $\text{1}$ and $\text{2}$, as well as those analogous imidazothiazinones $\text{3}$ and $\text{4}$, were used to calculate E_HOSE (Harmonic Oscillation Stabilization Energy). The problem of stability and chemical reactivity of compounds $\text{1}$ to $\text{4}$ is also discussed.