Total synthesis of (±)-Δ9(12)-capnellene via iterative intramolecular type-I-“Magnesium-ene” reactions

The marine triquinane sesquiterpene Δ⁹(¹²)-capnellene ($\text{1}$) was synthesised from 2,2,5-trimethyl-5-hexenal ($\text{2}$) by a sequence of all synthetic operations in 5% overall yield. The key steps 3 → 4 → 5 → 6 involve two intramolecular type-I-“Mg-ene” processes.     

Intramolecular diels-alder reaction with furan-diene: Total synthesis of (±)-11-ketotestosterone and (±)-adrenosterone

A novel D → BCD → ABCD route to 11 -keto steroids is reported involving a high yield stereoselective intramolecular Diels-Alder reaction of furan-diene $\text{12}$ in water as a key-step. The dienophilic side chain is readily introduced starting from $\text{8}$ via a sequence involving alkylation with ethyl ($\text{E}$)-3-ethoxy-4-iodo-2-butenoate, reduction and acid hydrolysis. The reduced adduct $\text{14}$ is further converted into (±)-adrenosterone ($\text{6}$) via $\text{24}$, the dienediolate equivalent of which is a known intermediate in corticosteroid synthesis.     

Stereoselective total syntheses of (±)-sinularene and of (±)-5-epi-sinularene via intramolecular type-I-“magnesium-ene” reaction

(±)-Sinularene ($\text{1}$) as well as (±)-5-epi-sinularene ($\text{9}$) were synthesised in a stereocontrolled manner from the norbornene $\text{2}$ in overall yields of 4% and 8%, respectively. The key step $\text{5}$ → $\text{6}$ involves a regio- and stereoselective intramolecular “magnesium-ene” reaction.     

Stekeospecific transformation of D-sugar to L-sugar in complex aminoglycoside. Synthesis of a kanamycin B analog having 2,6-diamino-2,4,6-trideoxy-L-arabino-hexopyranose

A 4′-ene derivative of kanamycin B ($\text{4}$) was derived from the epoxide ($\text{1}$) by oxidative elimination of the 4′-phenylseleno group into the allylic alcohol ($\text{3}$). The title compound, 0-(2,6-diamino-2,4,6-trideoxy-β-L-arabino-hexopyranosyl)-(1→4)-0-[3-amino-3-deoxy-α-D-glucopyranosyl-(1→6)]-2-deoxystreptamine ($\text{6}$) was obtained from $\text{4}$ by stereospecific hydrogenation followed by removal of the masking groups, changing the D-sugar moiety of the 4-0-glycoside portion into an L-sugar.     

The regiochemistry of intramolecular n-alkenylnitrone additions: preparative and mechanistic implications

The opposite regiochemistry, observed for the reactions $\text{7a}$ → $\text{8a}$ and $\text{7d}$ → $\text{8d}$, as compared with additions $\text{7b}$ → $\text{9b}$, $\text{7c}$ → $\text{9c}$ and $\text{7e}$ → $\text{9e}$, supports the hypothesis that in the transition state of nitrone-olefin additions the new C,C bond is more advanced than the C,0, bond. Further examples show the superimposition of substituent effects on this intramolecular control.     

Intramolecular silyl migration in the singlet oxygenation of 2-methyl-5-trimethylsilylfuran

Tetraphenylporphyrin-sensitized photooxygenation of 2-methyl-5-trimethylsilylfuran ($\text{4}$) affords quantitatively trimethylsilyl 2-oxo-4-pentenoate ($\text{5}$), presumably via intramolecular Baeyer-Villiger rearrangement of the intermediary dioxirane ($\text{3a}$).     

On the decay of the ozonide radical in aqueous alkaline solutions

In flash photolysis of an oxygenated aqueous potassium persulphate solution at pH 12.5 the decay of the ozonide radical has been found to follow $\text{3}\text{2}$ order kinetics which has been explained by reactions O^?₃ + O^? ? 2 O^?₂ and O^?₃ + HO₂ → 2 O₂ + OH^?     

Studies on the syntheses of heterocyclic and natural compounds. Part 939: An efficient and stereoselective synthesis of des-a-ring steroids—potential intermediates to estradiol,cortisone and progesterone

A stereoselective synthesis of des-A-ring steroids $\text{9}$ and $\text{17}$ has been achieved by an intramolecular cycloaddition of 3-isopropenyl-5-(4-methoxybenzocyclobutenyl) pentan-2-one-2-ethylene ketal $\text{7}$ and 1-(4-methoxy-benzocyclobutenyl)-4-methylpent-4-en-3-ol $\text{16}$, respectively.     

Trimethymetall-urotropinaddukte des aluminiums,galliums, indiums und thalliums

Reactions of urotropine (C₆H₁₂N₄) with trimethylmetal derivatives of Al, Ga, In und Tl in various ($\text{1}\text{1}$$\text{1}\text{4}$) molar ratios lead to stable and monomeric $\text{1}\text{1}$, $\text{1}\text{2}$ or $\text{1}\text{3}$ adducts in good yields, but no $\text{1}\text{4}$ addition product could be isolated. The vibrational spectra (IR and Raman) of all compounds are recorded and partly assigned. Some characteristic frequencies of the C₆N₄-skeletons clearly show the symmetry changes in the series of the $\text{1}\text{1}$ → $\text{1}\text{2}$ → $\text{1}\text{3}$ adducts (C_3ν → C_2ν → C_3ν). The X-ray structure determinations of C₆H₁₂N₄·.GaMe₃ (MeCH₃) and C₆H₁₂N₄·.2GaMe₃, are in good agreement with the vibrational spectra. Both compounds crystallize in monoclinic space groups (P2₁ and C2/c). The GaN distances are around 214 pm, and the values for the C₆N₄-skeletons are not significantly different from those for free urotropine.     

On the stereochemistry of photoaddition between α,β-unsaturated ketones and olefins. III.

The α,β-unsaturated ketone $\text{1}$ yields with allene the photocycloadduct $\text{3}$ predicted by our empirical photoaddition rule and the byproduct 7. The formation of this material may be rationalized by the sequence $\text{1}$ → $\text{4}$ → $\text{5}$ → $\text{6}$ → $\text{7}$. The isomeric ketone $\text{2}$ is unreactive under the same conditions, since α addition is prohibited by the rule and β addition is severely blocked.     

Synthesis of 3,3,3-trifluoropropionic and 4,4,4-trifluoro-2-ketobutyric acids

Trifluoroethyl cyclohexyl ketone ($\text{4}$) is prepared by acylation of difluoroethylene ($\text{2}$) with cyclohexanecarboxylic acid chloride ($\text{1}$), followed by Cl→F exchange with potassium fluoride in the presence of triethylbenzyl- ammonium chloride. Bayer-Villiger oxidation of ketone ($\text{4}$) with trifluoroperacetic acid gives cyclohexyl trifluoropropionate ($\text{5}$). 3,3,3-trifluoropropionic acid ($\text{6}$) is obtained by treatment of ($\text{5}$) with trimethylsilyl iodide. Condensation of 2,2,2-trifluorodiazoethane ($\text{7}$) with ethyl glyoxylate ($\text{8}$) gives mainly ethyl 4,4,4-trifluoro-2-ketobutyric acid ester ($\text{9}$) which leads after hydrolysis to the corresponding acid ($\text{12}$).     

4,6-Thioanhydro-hexopyranosides,synthesis and chemical behaviour of methyl 2-0-p-toluenesulfonyl-4,6-thioanhydro-α-d-gulopyranoside

Methyl 4-0-benzoyl-6-bromo-6-deoxy-α-D-glucopyranoside ($\text{1}$, Figure 1) was converted, via the corresponding ditosylate $\text{2}$, into methyl 2,3-di-0-p-toluenesulfonyl-4-0-benzoyl-6-S-acetyl-6-thio-α-D-glucopyranoside ($\text{3}$) by a selective nucleophilic displacement of 6-bromo-group with thioacetate. Unexpectedly, on treating the compound $\text{3}$ with an excess of sodium methoxide in benzene-methanol (1:1) at room temperature, methyl 2-0-p-toluenesulfonyl-4,6-thioanhydro-α-D-gulopyranoside ($\text{4}$) was obtained in a yield of 84%. In order to determine the structure of the relatively unstable oily product $\text{4}$, some stable crystalline derivatives ($\text{5}$, $\text{6}$ and $\text{7}$) were prepared. Detailed analysis of the ¹H-NMR-spectra (200 MHz) of $\text{6}$ and $\text{7}$ gave the conclusive evidence for the structure of $\text{4}$ A self-imposing mechanism of the clean and smooth transformation of $\text{3}$ to $\text{4}$ is proposed, involving: a) formation of $\text{9}$ (Figure 2) as a crucial intermediate and b) a highly regioselective epoxide opening in $\text{9}$ (at C-4) by an intramolecular nucleophilic attack of the mercaptide anion from C-6.     

Syntheses of enantiomeric dihydropyrans through stereocontrolled intramolecular cycloaddition

Reaction of the cyclic 1, 3-dicarboxylic acid derivatives ($\text{1}$), ($\text{2}$) and ($\text{3}$) with (R)- or (S)-citronellal ($\text{4}$/$\text{5}$) gives the enantiomeric tricyclic dihydropyrans ($\text{10}$), ($\text{11}$), ($\text{12}$) and ($\text{13}$), probably via a 100% stereocontrolled intramolecular cycloaddition.     

Cationic polar cycloaddition with chloromethyl phenyl sulfides

Chloromethyl phenyl sulfides $\text{3}$ underwent [4⁺ +2] type polar cyclo-additions with styrene, trans-stilbene, and phenylacetylene in the presence of stannic chloride to afford the thiochroman $\text{4}$, $\text{5}$ and thiochromen derivatives $\text{6}$. Under the same reaction conditions, N-allyl-α-chloro-α-(phenylthio)acetamide ($\text{7}$) gave the intramolecular cycloaddition product $\text{8}$.     

Inter vs intramolecular amidoalkylations of aromatics - a new synthesis of oxindoles,isoquinolones and benzazepinones

A new synthesis of oxindoles ($\text{8}$) isoquinolones ($\text{5}$) and benzazepinones ($\text{10}$) by the intramolecular amidoalkylation of aromatic amides of bismethoxycarbonylaminoacetic acid ($\text{4}$, $\text{7}$, $\text{9}$) is described.     

Dependence of transmission of conjugation through cyclopropane ring into vinyl group on electron demand of substituent

The placement of a methoxycarbonyl or a cyano group on the cyclopropane ring in spiro-vinylcyclopropanes ($\text{7a}$, $\text{7b}$) causes a drain of electrons from the vinyl group through the ring into the electron demanding substituent, precluding their [2+2]cycloaddition with TCNE but not with the stronger electrophilic olefin CSI ($\text{7}$ → $\text{8}$), whereas the placement of a hydroxymethyl group renders the vinyl group reactive toward TCNE ($\text{9}$ → $\text{13}$).     

Fluorocarbon derivatives of nitrogen. Part 10. Preparation of heptafluoro- and 1-chlorohexafluoro-2-nitrosopropane,and conversion on the latter to chloropentafluoroacetone oxime

Details are given for the preparation of heptafluoro-2-nitrosopropane and 1-chlorohexafluoro-2-nitrosopropane $\text{via}$ the routes CF₃CFCF₂ → [with CsFR_FCO₂Ag (R_F = CF₃, nC₃F₇)] (CF₃)₂CFAg → (with NOCl) (CF₃)₂CFNO and CF₃CFCF₂ → (with CsClNOCl) CF₃(CF₂Cl)CFNO, respectively, and for conversion of the latter nitroso-compound to chloropentafluoroacetone oxime $\text{via}$ reduction with aqueous potassium hydrogen sulphite.     

The importance of spin relaxation in the delayed fluorescence of molecular crystals

Deactivation rate constants of spin-orbital excited Br atoms in the reactions Br(²P_{$\text{1}\text{2}$}) + O₂ → Br(²P_{$\text{3}\text{2}$}) + O₂ (k₁), and Br(²P_{$\text{1}\text{2}$}) + NO → Br(²P_{$\text{3}\text{2}$}) + NO (k₄) have been measured with a photodissociative IBr laser on the electronic transition ²P_{$\text{1}\text{2}$}?²P_{$\text{3}\text{2}$} in the Br atom (λ = 2.7 μm). The values obtained are (6.4 ± 1.8) × 10^?14 cm³ s^?1 and (1.9 ± 0.6) × 10^?12 cm³ s^?1, respectively. Comparison with published data leads to the conclusion that, contrary to a widely accepted point of view, the high rate constants for the quenching of excited halogen atoms are due to resonant energy transfer processes and not to the paramagnetic nature of the quencher.     

Synthesis with immobilized enzymes of two trisaccharides,one of them active as the determinant of a stage antigen.

Glycosidation of disaccharides I and III with a system of five immobilized enzymes gave excellent yields of trisaccharides $\text{β-D}$-Gal-(1→4)-$\text{β-D}$-GlcNAc-(1→6)-$\text{D}$-Gal ¦ the I(Ma) determinant ¦ and $\text{β-D}$-Gal-(1→4)-$\text{β-D}$-Glc-NAc-(1→3)-$\text{D}$-Gal, on the milimole scale.     

Monoclinic-trigonal transition in some MI3M′III(XO4)3 compounds: The high temperature form of (NH4)3In(SO4)3

The high-temperature form of (NH₄)₃In(SO₄)₃ is rhombohedral, R3c, with a = 15.531 (12), c = 9.163 (8)Å, Z = 6. The structure was solved to R = 0.023 for 570 independent reflections measured at about 140°C. The structure is built up of [In(SO₄)₃]_∞ columns extending along the c axis and composed of InO₆ octahedra and SO₄ tetrahedra linked together; this arrangement is very similar to that found in the low-temperature form. To explain the transition mechanism, the existence of an intermediate phase of point symmetry $\text{3}$ is postulated and the whole sequence of possible forms would be $\text{2}\text{m}\text{→}\text{3}\text{→ 3m →}\text{3}\text{m}$. This last phase would be the prototypic structure of the possibly ferroelastic low-temperature modification, which can apparently exist only with nonspherical monovalent cations.