Directed metallations of 4-ethylidenetetronic acid and its derivatives as a synthetic entry to natural 4-oxy-2-furanones

Lithium diisopropylamide (LDA) removes the α-proton from the O-methyl tetronic acid (2$\text{b}$) leading to the vinylic carbanion (12), whereas treatment of the trimethylsilyl derivative (14) with LDA, followed by reaction with aldehydes gives products resulting from both γ? and ε-addition; the directed metallations provide access to a range of 4-oxy-2-furanone derivatives found amongst natural products.     

Naturally occurring 5-methyoxy-3(2H)-furanones. Re-assignment of structures to the aspertetronin group of natural products

Synthetic and spectroscopic investigations establish that the aspertetronin (also known as gregatin and graminin) group of natural products isolated from $\text{Aspergillus}$ and $\text{Cephalosporium sp}$., has the 5-methoxy-3(2H)-furanone structure (4) rather than the previously assigned O-methyl tetronic acid structure (3).     

Regiospecific alkylation of tetronic acids : Formation of 4-alkoxy-5H-furan-2-ones and 2-alkoxy-5H-furan-4-ones

2-Alkoxy-5$\text{H}$-furan-4-ones (7,8) and 4-alkoxy-5$\text{H}$-furan-2-ones (4,5) were prepared regiospecifically and in high yields from tetronic acids (4-hydroxy-5$\text{H}$-furan-2-ones) (2) in the first case by acetylating the 4-OH group and then reacting with trialkyloxonium tetrafluoroborate, and in the second case by alkylating tetrabutylammonium tetronates with dialkyl sulfate, respectively. Direct alkylation of tetronic acids with trialkyloxonium tetrafluoroborate gave in four cases regiospecific 2-O-alkylation, in one case 4-O-alkylation and in two other cases mixtures of 2- and 4-alkoxy derivatives.     

Etude des reactions des diazoderives avec les cycloimmonium ylures-I : Action des sels de diazonium sur quelques pyridinium - ylures

The synthesis of cycloimmonium salts of the type $\text{7}$, $\text{8}$ and the corresponding cycloimmonium ylides $\text{9}$, $\text{10}$ are reported. In the reaction with diazonium salts $\text{11}$, $\text{12}$ the pyridinium monosubstituted carbanion ylides $\text{9}$, $\text{10}$ give the pyridinium disubstituted carbanion ylides $\text{17}$ – $\text{20}$. These are new types of isolable stable ylides. The synthesis involves the formation “in situ” of ylides $\text{9}$, $\text{10}$ which are bonded by their nucleophile ylide carbon atom to the nitrogen atom in diazonium salts. The intermediat formation of cycloimmonium salts $\text{13}$ – $\text{16}$ must be accepted. The structures of all compounds presented in this paper have been established by using elementary analysis, IR and ¹H-RMN spectra.     

Total synthesis of (+)-prelog-djerassi lactonic acid

Optically active Prelog-Djerassi Lactonic Acid $\text{1}$ was synthesized from D-glucal: the crucial point being the elaboration of the carboxylic group as shown in eq. 1 and 2 which involve the sequential process [i] asymmetric addition of methyl anion onto the hetero-olefin 2, [ii] trapping the carbanion intermediate $\text{3}$ [E=Li to SePh] and [iii] oxidative hydrolysis of $\text{3}$$\text{via}$ sila-pummerer rearrangement into $\text{4}$.     

Diethyl[trimethylsilylethoxymethyl]phosphonat - ein neuartiges reagens für variable aufbaustrategien von carbonyl-, α-hydroxycarbonylverbindungen und vinylphosphonaten

The carbanion of $\text{2}$ prepared by means of s-BuLi can be transformed stepwise with various electrophiles to the phosphonates $\text{3}$–$\text{5}$, opening via $\text{6}$ new approaches to carbonyl compounds $\text{7}$, phosphates of α-hydroxycarbonylderivatives $\text{8}$ and vinylphosphonates $\text{9}$.     

Novel (4 + 1) fragment combination approach to chiral cyclopentanoids from tartaric acid

A $\text{chiral}$ cyclopentanoid building block $\text{29}$ has been synthesized in “one pot” cyclization process from epoxides $\text{22}$ - $\text{25}$ (which are readily accessible from (R,R)-(+) tartaric acid) with the carbanion derived from phenylthioacetonitrile (PhS-CH₂-CN).     

A theoretical investigation of α-substituents on the structure,proton affinities and inversion barriers of silyl anions

Geometries, optimised at the double-zeta level, are reported for silanes SiH₃X and silyl anions SiH₂X^? where X = H, BH₂, CH₃, NH₂, OH and F. The anions are pyramidal with larger out-of-plane angles than their carbanion analogues and inversion barriers are large, varying from 34.3 $\text{kcal}\text{mole}$ for X = H up to 57.3 $\text{kcal}\text{mole}$ when X = F. The silylborane anion is planar at both boron and silicon and has a Si-B bond length shorter by 0.15 than in silylborane. Silyl anions are more stable than methyl anions by between 55 and 66 $\text{kcal}\text{mole}$.     

Synthesis of macrocyclic terpenoids by intramolecular cyclization XIII. : Stereoselective synthesis of (±)-cubitene,a component of defense secretion of termites

Stereoselective synthesis of cubitene ($\text{1}$), a novel diterpene isolated from defense secretion of termites, has been accomplished using an intramolecular reaction of α-sulfenyl carbanion with epoxide. Hydride reduction of the ketone $\text{11}$ obtained by Claisen rearrangement occurred in unexpectedly high stereoselectivity yielding the chlorohydrin $\text{12}$ with the desired stereochemistry.     

Syntheses of PGJ2 type analogues: 16-hydroxy-11-oxo-Δ5,9,12,14-prostatetraenoic acid t-butyl ester and its related derivatives

PGJ₂ analogues, the title compound ($\text{8c}$) and its related derivatives ($\text{8a}$, $\text{8b}$), were synthesized $\text{via}$ the three-component coupling process involving 1,4-addition reaction of phenylsulfinylallylic carbanion ($\text{2}$′) to cyclopentenone derivative ($\text{1}$) followed by trapping the generated enolate with aldehyde ($\text{3}$).     

Palladium-catalyzed asymmetric cyclization of methyl (E)-oxo-9-phenoxy-7-nonenoate and its analogs

Asymmetric cyclizations of methyl (E)-3-oxo-9-phenoxy-7-nonenoate ($\text{1}$) or methyl (E)-3-oxo-9-(methoxycarbonyl)oxy-7-nonenoate ($\text{4}$) without added base were carried out in the presence of a catalytic amount of palladium(II) acetate and chiral diphosphine as ligands. Allylic carbonate $\text{4}$ reacted by use of Pd(OAC)₂-(S)-(R)-BPPFA at room temperature to give (R)-3-vinylcyclohexanone ($\text{3}$), after decarboxylation, in up to 48% e. e.     

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.     

Bicyclomycin synthetic studies: utilization of bridgehead carbanions

The synthesis of a bicyclomycin model compound ($\text{19}$) has been achieved utilizing an efficient hydroxylation of a simple bicyclic bridgehead carbanion.     

New Phenyl propanoids having weak piscicidal action and the related compound: wutaiensol,wutaiensal, wutaialdehyde,and methyl demethoxywutaiensate

The structures of three new prenylphenyl propanoids, wutaiensol ($\text{1}$), wutaiensal ($\text{2}$), and methyl demethoxywutaiensate ($\text{4}$) were established by correlating with S-rutaretin methyl ether ($\text{9}$) or S-marmesin ($\text{24}$) by chemical means. The structure of wutaialdehyde ($\text{3}$), a related compound, was also established by total synthesis of the racemate and by correlating with $\text{1}$. Preliminary piscicidal test on these compounds disclosed that $\text{2}$ and $\text{4}$ are weakly bu distinctly positive.     

Successive methyl migrations occurring in the acid treatment of 1-epoxyethyl-1,2,2-trimethyl-cyclopentane derivative

Acid treatment of (IR, 3S,1′S)-1-(1′,2′-Epoxyethyl)-1,2,2-trimethyl-3-acetoxymethyl-cyclopentane $\text{6}$) has been shown to yield three products ($\text{8}$, $\text{9}$, $\text{10}$), among which $\text{8}$ and $\text{9}$ are 1-oxa-bicyclo[3.3.0]octane derivatives formed $\text{via}$ successive methyl migrations followed by an oxorane ring closure.     

Silicon in organic synthesis. 12. trans-1-benzenesulfonyl-2-(trimethylsilyl)ethylene,a Diels-Alder dienophile equivalent of acetylene and monosubstituted acetylenes

$\text{trans}$-1-Benzenesulfonyl-2-(trimethylsilyl)ethylene and its 1,2-$\text{d}$₂ derivative enter into Diels-Alder cycloaddition to give products which are smoothly eliminated with fluoride ion. Alkylation of the α-sulfonyl carbanion can precede elimination, such that synthetic equivalents for HCCH, HCCD, DCCD, RCCH, and RCCD are now available.     

Backbone rearrangements of methyl (-)-kaur-9(11)-en-19-oate and its epoxide: structures of two diterpenes of a new skeletal type

cleavage of the epoxide ($\text{2}$) of methyl (-)-kaur-9(11)-en-19-oate ($\text{1b}$) with boron trifluoride-ether in benzene and in acetic anhydride yielded ($\text{3a}$) and ($\text{3b}$), respectively. On epoxidation with $\text{m}$-chloroperbenzoic acid in the presence of $\text{N}$-nitrosomethyl urea, ($\text{1b}$) suffered a backbone rearrangement to form ($\text{6}$).     

Chirale synthese von (+)-lycoricidin

The synthesis of (+)-lycoricidine from D-glucose is described. Addition of the carbanion $\text{11}$ to the nitroolefine $\text{10}$ yields the adduct $\text{12}$ + $\text{13}$, from which crystalline lactone $\text{16}$ with $\text{muco}$-configuration in the cyclitol-ring can be isolated after hydrolysis and cyclization. Rearrangement to the lactam $\text{17}$ and elimination yields the (+)-lycoricidine.     

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.     

The absolute configurations of (+)-thalictrifoline and (+)-corydalic acid methyl ester. Total synthesis of (+)-thalictrifoline.

(+)-Thalictrifoline ($\text{3}$) has been synthesized from an optically resolved (+)-8-oxo-13-carboxytetrahydroprotoberberine ($\text{13}$) whose absolute configuration was established by correlation with (+)-$\text{18}$. This determines the absolute configurations of (+)-thalictrifoline ($\text{3}$) as 13R, 14R aria (+)-corydalic acid methyl ester ($\text{9}$) as 3R, 4R.