Asymmetric allylsilane-mediated carbocyclization: A highly enantiospecific synthesis of (1S, 2S)-(+)-2-methyl-3-cyclopenten-1-ol

An enantiospecific synthesis of the title compound is described which involves the TiCl₄-promoted cyclization of the chiral allylic silane having formyl group, which was obtained via the Claisen rearrangement of ($\text{R}$, $\text{E}$)-1-trimethylsilyl-1-buten-3-ol.     

Pheromone XXXVII. Eine stereospezifische synthese der komponenten des sexualpheromons von antherea polyphemus, (E)-6,(Z)-11-hexadecadienylacetat und (E)-6,(Z)-11-hexadecadienal.

Starting from the aldehydes $\text{2}$ and $\text{9}$ the acetylene $\text{16}$ is prepared via the borane $\text{15}$ by means of a combined Wittig reaction-hydroboration reaction sequence. $\text{16}$ may be converted into the (E)-6,(Z)-11-hexadecadienylacetate ($\text{18}$) and the corresponding aldehyde $\text{19}$. The synthetic route proceeds with high stereospecifity (isomeric purity of $\text{18}$ and $\text{19}$ ? 97%).     

Kationische cyclisierung von (Z)-und (E)-1,3-dimethyl-2-(3-hexenyl)-2-cyclohexenol

The cationic cyclization of the carbinol $\text{3a}$(Z) occurred stereoselectively and resulted in a mixture of the hydrindane $\text{4a}$ and the octalin $\text{5a}$, both with $\text{trans-}$configuration of side chain and angular methyl group. Cyclization of $\text{3b}$(E) yielded in $\text{4b}$ and $\text{5b}$, both with $\text{cis}$-configuration. The structure of $\text{4a}$,$\text{5a}$ was proved by transformation to the diketones $\text{8}$,$\text{9}$.     

A stereocontrolled synthesis of Z and E terminal dienes from pinacol E-1-trimethylsilyl-1-propene-3-boronate

Pinacol $\text{E}$-1-trimethylsilyl-1-propene-3-boronate reacts with aldehydes to form (±)-($\text{R}$*,$\text{S}$*)-3-trimethylsilyl-4-hydroxy-1-alkenes, which can be deoxysilylated stereoselectively to either 98% $\text{Z}$ or 99% $\text{E}$ 1,3-dienes, including the separate components of the red bollworm moth pheromone.     

5-Exo-Trig vs 6-Endo-Trig α-acyliminium ion-olefin cyclisations stereoselective synthesis of 7-(1-formyloxy-pent-1-yl)-1-aza-4-oxa-spiro[4.5]decane-2-ones

The two C₆, C₇$\text{trans}$ substituted title compounds have been synthesized via stereoselective 5-$\text{Exo}$-Trig ringclosures starting from (E)-resp. (Z)-4-nonene-1-yl bromide and 3,5-morpholinedione.     

1-Benzenesulfonyl-2-trimethylsilylethane and 1-benzenesulfonyl-1-chloro-2-trimethylsilylethane; efficient reagents for sulfonyl-α-vinylation

1-Benzenesulfonyl-2-trimethylsilylethane and 1-benzenesulfonyl-1-chloro-2-trimethylsilylethane are convertable to 1-benzenesulfonyl-1-chloro-1-substituted-2-trimethylsilylethanes which undergo elimination by fluoride ion to give phenyl $\text{α}$-substituted-vinyl sulfones.     

Preparation of optically active allylsilanes by catalytic asymmetric hydrosilylation of 1-arylbutadienes1

Asymmetric hydrosilylation of 1-arylbutadienes with trichlorosilane in the presence of a chiral ferrocenylphosphine-palladium catalyst gave optically active allylsilanes, ($\text{Z}$)-1-aryl-1-silyl-2-butenes and their regioisomers.     

Homoenolate dianions of secondary amides via tin/lithium exchange

Treatment of N-phenyl- a well as N-methyl-3-(tri-bar|n-butylstannyl)-propionamide with 2 equiv of bar|n-butyllithium in the presence of 1,4-diazabicyclo[2.2.2]octane at ?78°C in tetrahydrofuran produced the corresponding dilithio derivatives (homoenolate dianions) $\text{4}$ and $\text{8}$ respectively. Reaction with various electrophiles (1 equiv) gave the terminally substituted amides in good yields.     

Highly stereocontrolled synthesis of (2e,4z)-dienic esters by alumina catalyst

Thermal treatment of β-allenic esters ($\text{2}$) with alumina catalyst in aprotic solvents yielded (2E,4Z)-dienoic esters ($\text{3}$) in 57-58% yield with 91-100% stereoselectivity.     

A short and efficient synthesis of 4-hydroxy-5-(1-hydroxyalkyl)-γ-butyrolactones

The cycloaddition of α,β-epoxyaldehydes or ketones ($\text{2}$) with the ketene acetal MeHC=C(OMe)₂ ($\text{1}$) gives epoxyoxetanes ($\text{3}$) in high yields. Without isolation they can be transformed into 4-hydroxy-5-(1-hydroxyalkyl)-γ-butyrolactones ($\text{6}$) via the epoxy esters $\text{4}$ and trihydroxy esters ($\text{5}$). The lactones $\text{6}$ appear to be valuable precursors for the synthesis of 5-(1-hydroxyalkyl)-3-methyl-2-5H-furanones ($\text{7}$) and 3-methyl-5-ylidene-2-5H-furanones ($\text{8}$)     

Preparative methods for (Z)-2-methoxy-1-phenylthio-1,3-butadienes. Rearrangement during copper(I)-induced elimination of thiophenol from some γ,δ-unsaturated thioacetals

(Z)-2-Methoxy-1-phenylthio-1,3-butadienes which are substituted with an alkyl group at the 4-position are not preparable by copper(I)-induced elimination of thiophenol from 4-alkyl-2-methoxy-1,1-bis(phenylthio)-3-alkenes; a 2-step stereospecific synthesis of one such diene ($\text{18}$) is described.     

A diastereoselective synthesis 1-trimethylsilyl-(E)-1,3-alkenynes and a simple synthesis of alkyl trimethylsilylethynyl ketones via organoboranes

A convenient, novel diastereoselective synthesis of 1-trimethylsilyl-(E)-1,3-alkenynes and a convenient synthesis of alkyl trimethylsilylethynyl ketones based on Z-1-bromo-1-alkenylboronate esters are developed. α-Bromo-(Z)-1-alkenylboronate esters readily available using literature procedures smoothly undergo a reaction with trimethylsilylethynyllithium (derived from the deprotonation of trimethylsilylethyne with n-butyllithium) in tetrahydrofuran to provide the corresponding ‘ate’ complexes. These ‘ate’ complexes undergo intramolecular nucleophilic substitution reactions to afford the corresponding (E)-1-alkenylboronate esters containing trimethylsilylethynyl moiety which upon protonolysis with acetic acid provide the corresponding 1-trimethylsilyl-(E)-1,3-alkenynes in good yields (70-82%) and in high stereochemical purities (>98%). These intermediates upon oxidation with hydrogen peroxide and sodium acetate afford the corresponding alkyl trimethylsilylethynyl ketones in good yields (66-78%).     

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).