Christian Margot

Facile isomerization of oxiranes to allyl alcohols by mixed metal bases

Abstract The mixture of lithium diisopropylamide and potassium tert-butoxide (“LIDAKOR reagent”) promotes smooth ring opening of oxiranes to afford allyl alcohols with good to excellent yields. Internal epoxyalkanes and large size epoxy-cycloalkanes give preferentially or exclusively trans-alkenols. The regio- and stereochemistry of the ring opening reaction are essentially the consequence of syn-periplanar elimination mechanisms.

A regio- and stereocontrolled access to 2,4-dienols by amide/alcoholate-promoted ring-opening of dihydro-pyrans

Dihydropyrans I (R = R1 = H, R2 = H, Me, CH2CH2CH:CMe2; R = Me, CH2CHMe2, R1 = H, R2 = Me; R = R2 = H, R1 = CH:CMe2), when treated with LiN(CHMe2)2-KOCMe3, underwent smooth ring cleavage through b-elimination to give dienols (Z)-HOCHRCR1:CR2CH:CH2. Methylenetetrahydropyrans II (R3 = Me, CH2CHMe2) gave HOCHR3CH2C(CH:CH2):CH2, while II (R3 = H) gave (E)-HOCH2CH:CMeCH:CH2. Other cyclic or acyclic homoallylic ethers reacted similarly. [on SciFinder (R)]

Mixed metal bases as promoters of 1,4-eliminations

When treated with the LIDAKOR mixt., allyl type ethers very readily undergo 1,4-elimination to afford conjugated dienes (E)-H2C:CHCH:CH(CH2)4Me, H2C:C(:CH2)CH2CH2CH:CMe2, H2C:CHCH:CHOMe. In typical cases, the reaction is brought about stereo- and regioselectively, e.g., (E)-H2C:CHCH:CH(CH2)4Me and H2C:C(:CH2)CH2CH2CH:CMe2). Under suitable conditions, lithium dimethylamide or even lithium diisopropylamide adds to the dienes generated in situ thus leading to a variety of new allyl amines Me2C:CHCH2CH2C(CH2NMe2):CHMe, Me2CHCH2CH2CH:CMeCH:CHNMe2, and (Z)-MeCH:CHCH2N(CHMe2)2. [on SciFinder (R)]

1,2-Elimination of alcohol from homoallyl ethers under the influence of mixed metal bases

Abstract Lithium diisopropylamide in the presence of catalytic amounts of potassium tert-butoxide smoothly converts homoallyl or homobenzyl type ethers to dienes e.g. e.g., 1,3,5,26 or styrenes ( 2 ). γ,δ-Unsaturated acetals give 13-dienyl ethers e.g., 4 and 4-alkylidenetetrahydropyrans or dihydropyrans produce a variety of dienols ( e.g. , 6–17,20–22 ). - If there is a choice, the new double bond is formed with high trans -selectivity while the configuration of existing double bonds is retained. - The elimination mode is syn -periplanar and concerted, though E1cb like.

A new stereoselective synthesis of (Z)-9-tricosene, the sex attractant of the common housefly

Muscalure (9/tricosene) was prepd. very readily by an instant-ylid reaction of nonanal with Ph3P:CH(CH2)12Me or of (Z)-Me(CH2)7CH:CHCH2OAc with BrMg(CH2)11Me. (Z)-9-Tricosene was formed in a highly selective manner (.apprx.97.5) although it was difficult to assess the Z/E-ratio with accuracy. [on SciFinder (R)]

Biosynthetic, studies of marine lipids. 21. Experimental demonstration of a biosynthetic interconversion of cyclopropene sterols in the sponge calyx nicaeensis

Abstract In vivo isomerization of cyclopropenes has been demonstrated for the first time through feeding experiments of appropriately labeled cyclopropene sterols (1c-4c) in the sponge Calyx nicaeensis.

α-Deprotonated allyl ethers: Conformational mobility and conformational preferences

Tert-BuLi is best suited to accomplish an H-metal exchange at the a-position of g-alkyl branched allyl ethers. Rapid torsional equilibration occurs at the g-terminus of the deprotonated allyl unit, while the alkoxy group at the a-site has to occupy the exo position in order to minimize steric repulsions. Introduction of an alkoxy group into the terminal position of a g-branched 2-alkenyllithium lowers the barrier to torsional isomerization slightly (by a few kcal/mol). [on SciFinder (R)]

Biosynthesis of three cyclopropene-containing sterols in the sponge Calyx niceaensis

As shown by a series of radiolabelling experiments in the sponge Calyx niceaensis, the cyclopropane sterol dihydrocalysterol (3), itself a metabolic product of 24-methylenecholesterol (1), undergoes formal cis-dehydrogenation to the cyclopropene 24H-isocalysterol (6).