Stereoselectivity in cycloaddition of phenylglyoxylonitrile oxide to 7-substituted norbornadienes and 8-substituted 2-azabicyclo[3.2.1]oct-3,6-dienes

The cycloaddition of phenylglyoxylonitrile oxide to the 7-substituted norbornadienes $\text{1}$a-c gives predominantly the endo isomers, but that to the 8-substituted 2-azabicyclo[3.2.1]oct-3,6-dienes $\text{2}$a,b the exo isomers.     

Fluorinated chromenes 1: 2,2,2-trifluoroethoxy precocene analogs and their corresponding 3,4-epoxides

Preparation of potential insect antijuvenile hormone agents 2,2-dimethyl-7-(2,2,2-trifluoroethoxy)-2H-chromene ($\text{3a}$), 6-methoxy-2,2-dimethyl-7-(2,2,2-trifluoroethoxy)-2$\text{H}$-chromene ($\text{3b}$) and 7-methoxy-2,2-dimethyl-6--(2,2,2-trifluoroethoxy)-2$\text{H}$-chromene ($\text{3c}$) and the corresponding 3,4-epoxides $\text{5a}$ and $\text{5b}$ is reported.     

Enantioselective microbial hydroxylation of bicyclo(2.2.1)heptane carbon skeleton

Bicyclo(2.2.1)heptane-7-carboxylic acid ($\text{9}$) and methyl bicyclo(2.2.1)hept-2-ene-7-$\text{syn}$-carboxylate ($\text{5}$) were microbiologically hydroxylated to give (1$\text{R}$)-2-hydroxy derivatives.     

Synthesis of 4′-amino-4′-deoxy analog of pantothenic acid

The synthesis of $\text{D}$- and $\text{L}$-N-(4-amino-3, 3-dimethyl-2-hydroxybutyryl)- β-alanine ($\text{7}$) is described. Compound $\text{7}$ is an analog of pantothenic acid in which the 4′-hyroxy group is replaced by amino group. The synthetic sequence leading to $\text{7}$ involved the synthesis $\text{D}$L-4-amino-3,3-dimethyl-2-hydroxybutyric acid and its resolution. Coupling of N-benzyloxycarbonyl N-hydroxysuccinimide ester ($\text{5}$) with β-alanine and followed by removal of the protecting group gave $\text{7}$.     

On the question of carbonyl oxide intermediates in the oxygen transfer by furan endoperoxides and bicyclic ozonides: intramolecular trapping experiments

On heating the furan endoperoxide ($\text{2}$) rearranges into the enol ester ($\text{4}$) and the bicyclic ozonide ($\text{3}$) affords instead the rearranged ozonide ($\text{7}$). The process ($\text{2}$) → ($\text{4}$) represents an intramolecular Baeyer-Villiger rearrangement presumably via the dioxirane (D-2), while the process ($\text{3}$) → ($\text{7}$) represents intramolecular trapping of the carbonyl oxide (C-3).     

O- versus N-methanesulphonylation and N-(methanesulphonyl)-methanesulphonylation with methanesulphonyl chloride

Depending upon the experimental conditions, t-butyl (1$\text{SR}$,5$\text{SR}$,7$\text{RS}$,8$\text{RS}$)-1-ethoxycarbonyl-8-hydroxy-2-oxa-6-azabicyclo[3.2.0]octane-7-carboxylate (2a) reacts with methanesulphonyl chloride to give predominantly the $\text{O}$-methanesulphonyl derivative (2b), the $\text{N}$-methanesulphonyl derivative (3a), or the $\text{N}$-(methanesulphonyl)methane-sulphonyl derivative (6a).     

Two chrome derivatives from the brown alga Zonariatournefortii

Two minor lipid components of the brown seaweed $\text{Zonaria}$$\text{tournefortii}$ were characterized as (all Z) - 5′,7′-dihydroxy-2′-nonadeca-4,7,10,13,16-pentenyl-chrome chromone ($\text{3}$) and 5′,7′-dihydroxy-2′-pentadecylchrome ($\text{4}$).     

The protection of uracil and guanine residues in oligonucleotide synthesis

The protection of uracil and 2-$\text{N}$-acyl guanine residues with 4-$\text{O}$-phenyl [or 4-$\text{O}$-(2,4-dimethylphenyl)] and 6-$\text{O}$-(2-nitrophenyl) groups as in $\text{7a}$ [or $\text{7b}$] and $\text{9}$, respectively, is described. These $\text{O}$-aryl protecting groups, which appear to withstand the usual conditions of oligonucleotide synthesis, may readily be removed by treatment with 2-nitrobenzaldoximate ions.     

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.     

Electrophile-mediated cyclizations in carbohydrate chemistry: synthesis of highly functionalized ribofuranose and ribopyranose compounds

Iodine-mediated cyclization of (Z)- and (E)-{=D}-ribohept-2-enonates $\text{1}$ and $\text{2}$ gave exclusively the β-ribofuranose and α-ribofuranose derivatives $\text{3}$ and $\text{4}$, respectively. Cyclization of the (Z)- and (E)-2-heptene-1-ol derivatives $\text{5}$ and $\text{6}$ gave ribofuranose products ($\text{7}$ and $\text{8}$) and a ribopyranose ($\text{9}$), respectively.     

Intramolecular Lewis-acid promoted (2+2) cycloadditions: An efficient total synthesis of (±)-coronafacic acid via an internal Diels-Alder reaction.

Internal (2+2) cycloaddition of the ester $\text{7}$ gave the cyclobutene $\text{8}$ in fair yield; cyclization of the readily derived trienone $\text{4}$ and hydrolysis produced coronafacic acid in 7% overall yield.     

3-Bromo-2-(tert-butylsulfonyl)-1-propene. A multi-coupling reagent Part 1.

3-Bromo-2-(tert-butylsulfonyl)-1-propene $\text{4}$ is easily available in two steps from allyl-tert-butylthioether $\text{5}$ (70% overall yield). It reacts with a great variety of carbanions to give functionnalized α, β-unsaturated sulfones of type $\text{7}$ in high yields. A second nucleophile (lithium cuprates) can then be added to compounds $\text{7}$ to furnish functionnalized sulfones of type $\text{3}$ (Y=SO₂-tert-butyl).     

New synthesis of benzo [a]quinolizidin-2-ones via protected 2-aryl-4-piperidones

A new synthesis of 9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-benzo aquinolizin-2-one ($\text{1a}$ and its 3-ethyl derivative $\text{1b}$ via the corresponding 2-(3,4-dimethoxyphenyl)-4-piperidone ethylene acetals $\text{7}$ is reported. Alkylation of 2-arylpipendires $\text{7}$ with 2-bromoethanol followed by oxidation of the resulting amino alcohols $\text{9}$ with oxalyl chloride and dimethyl sulfoxide afforded the aldehydes $\text{10}$, which were cyclized with hydrochloric acid to give 7-hydroxybenzo[α]quinolizidines $\text{11}$. The reduction of $\text{1}$ with trinethylsilane and subsequent acid hydrolysis led to benzo aquinolizidin-2-ones $\text{1}$.     

Pummerer reaction intermediate as an initiating function for cationic olefin cyclization

Treatment of N-(2-methyl-2-propenyl)-N-methyl-α-(methylsulfinyl)acetamide ($\text{6a}$) with trifluoroacetic anhydride caused the cationic olefin cyclization through a Pummerer reaction intermediate to give the six-membered lactams $\text{7}$ and $\text{8}$. Similar reaction converted N-2-butenyl-N-methyl-a-(methylsulfinyl)acetamide ($\text{6b}$) to the five-membered lactam $\text{9}$, and N-2-propenyl-N-methyl-α-(methylsulfinyl)- acetamide ($\text{6c}$) to the five-membered lactams $\text{11}$ and $\text{12}$.     

Regioselective synthesis of 4-alkylquinolines from quinoline via 1-ethoxycarbonyl-1, 2-dihydroquinoline-2-phosphonates

1-Ehtoxycarbonyl-1, 2-dihydroquinoline-2-phosphonates ($\text{3}$) were treated with n-butyllithium followed by alkyl halides to afford the corresponding 4-alkylated phosphonates ($\text{7}$) with complete regioselectivity in 67–97% yields. The phosphonates ($\text{7}$) were converted to 4-alkylquinolines ($\text{8}$) in ca. 50% yields by treatment with sodium iodide in HMPA or by alkaline hydrolysis in aqueous ethanol.     

New highly strained bridgehead imines, 2-azaadamant-1-ene and 4-azaprotoadamant-3-ene

An azaanalog of adamantene, 2-azaadamant-1-ene ($\text{1}$) and 4-azaprotoadamant-3-ene ($\text{7}$) were generated in the nonstatistical ratio via photolysis of 3-azidonoradamantane ($\text{2}$). The highly strained $\text{1}$ and $\text{7}$ could not be isolable but were trapped by MeOH. Acidolysis of $\text{2}$ was also reported, and discussed in comparison with the photolysis.     

Reaktion von trans-1-arylbutadienen und 1,1-diarylbutadienen mit tetracyanethylen (TCNE) und 2,2-bis(trifluormethyl)ethylen-1,1-dicarbonitril (BTF): kinetische studie

Kinetic data (substituent effects, solvent effects, activation parameter) are reported for the reactions of trans-l-arylbutadienes $\text{1}$ and 1,1-diarylbutadienes $\text{3}$ with TCNE $\text{4}$ and BTF $\text{5}$. (2+2)- and (4+2)-cycloadducts $\text{7}$ respectively $\text{9}$ can rearrange or undergo-cycloreversions with quite different reaction rates-depending on the substituent in the aryl-ring.     

Synthesis of “9-deazaadenosine”; A new cytotoxic C-nucleoside isostere of adenosine

The synthesis of 7-(β-$\text{D}$-ribofuranosyl)-4-amino-5H-pyrrolo[3,2-$\text{d}$]pyrimidine (9-deazaadenosine) $\text{9}$ is described. It involves base-catalyzed cyclization of N-carboethoxyenamine $\text{4}$ to give β- and α-ribosylated 3-amino-2-cyanopyrroles $\text{6}$ and $\text{7}$, respectively, followed by a one-step conversion to the desired pyrrolo[3,2-$\text{d}$]pyrimidine system.