Richard K. Haynes

HMPA-Mediated conjugate addition of alkyl- and phenylthioallyl anions to cyclopentenone

Abstract One equivalent of HMPA induces 1,4-addition of the title anions predominantly through the α -position to cyclopentenone in THF at −78°. In THF alone irreversible addition takes place to give mixtures comprising largely α and γ -1,2 products.

Preparation of stable, camphor-derived, optically active allylic sulfoxides

Abstract (+)-Camphor has been stereospecifically converted in three steps into a single isoborneol allyl sulfoxide derivative, which upon heating to 145° is quantitatively converted into its sulfoxide epimer; the anions of these compounds undergo stereospecific conjugate addition to cyclopent-2-en-1-one.

New reactions of triplet oxygen which avoid the spin barrier

The cation triphenylmethylium and the cation radical tris-(p-bromophenyl)ammoniumyl are effective catalysts for oxygenation of ergosteryl acetate (1; R = Ac) to the peroxide (2; R = Ac); the triphenylmethylium-catalysed reaction is a photo-oxygenation, whereas the cation radical reaction is thermal. Several other ‘forbidden’ additions of triplet oxygen to cisoid dienes have been demonstrated. A number of cation radicals have been examined for catalytic oxygenation ability. Ergosteryl acetate can also be converted into its peroxide by triplet oxygen in the presence of various Lewis acids.Two mechanisms for overcoming the spin barrier for triplet oxygen addition have been defined by experimental work. A mechanistic interpretation of the facts is proposed.

The diastereospecific aprotic conjugate addition reactions of carbanions derived from allylic sulfoxides and allylic phosphine oxides

Abstract The title carbanions undergo conjugate addition to cyclic enones in THF to deliver vinylic sulfoxides and vinylic phosphine oxides as single diastereomers.

A route to prostaglandin precursors from 1-(phenylthio)-2-octenyllithium.

The enolates generated by the conjugate addition of 1-(phenylthio)-2-octenyllithium to 4-tert-butoxycyclopent-2-en-1-one and <-crotonolactone react with methyl 7-halohept-5-ynoates in the presence of Ph3SnCl to deliver products which may be converted into prostaglandin precursors.

The diastereospecific aprotic conjugate addition reactions of allylic anions-mechanistic aspects.

Abstract A ten-membered cyclic “chair-chair” - or “ trans -decalyl”-like TS is proposed to account for the diastereospecific aprotic conjugate addition reactions of allylic carbanions bearing polar, charge-stabilizing groups.

Trimethylsilyl triflate catalysed Diels-Alder reaction of TMS ethers of conjugated dienols with cyclic enones: Evidence for an endo transition state, and first application to synthesis of enantiopure octalins

Abstract The AlCl3 catalysed ‘ionic’ Diels-Alder (DA) reaction of 6-methyl-2-cyclohexenones with 3,5-hexadien-1-ol in dichloromethane gives a trans-fused octalin hemiacetal with a β-equatorial methyl group and an axial hydroxyl. In contrast, trimethylsilyl triflate (TMSOTf, 5 mol%) at −20 °C in acetonitrile catalyses the DA reaction to give the trans-fused adduct acetal, whose controlled hydrolysis gives the hemiacetal with an α-axial methyl group. The adduct is thereby differentiated from the AlCl3 DA adduct, and may be converted into the latter by treatment with p-toluenesulfonic acid in aqueous THF or by AlCl3 in dichloromethane. In similar fashion, TMSOTf provides full acetal adducts from 2-cyclohexenone, 2-cycloheptenone and methyl vinyl ketone. The optically active enone acetal derived from (1R,2R)-1,2-diphenyl-1,2-ethanediol and 2-cyclohexenone gives a racemic acetal adduct derived from the TMS ether of hexadienol. The TMS ether of a mixture enriched in the 3E-isomer of (2R,5E)-2-methyl-3,5-heptadien-1-ol in acetonitrile containing TMSOTf (10 mol%) at −20 °C with 6-methyl-2-cyclohexenone gives the trans-fused acetal adduct, hydrolysis which provides the corresponding octalin hemiacetal as a single enantiomer. Similarly, the mixture enriched in the 3E-isomer of (2S,5E)-2-methyl-3,5-heptadienol TMS ether is converted by way of the octalin acetal into the octalin hemiacetal, enantiomeric with the foregoing product. The reactions are thereby shown to proceed via endo transition states.

The preparation and reactions of dienol ester and dienol ester derivatives of hagemann's ester and its t-butyl analogue

Abstract The efficient conversion of Hagemanns ester and its t-butyl analogue into dienol ethers and dienol esters, and reactions of the derived dienolates with electrophiles is described.

Peroxide–diene oxygen transfer reactions induced by titanium tetrachloride

Catalysis of the reaction between triplet oxygen and ergosteryl acetate (I) by titanium tetrachloride unexpectedly affords 6α-chloro-5-hydroxy-5α-ergosta-7,22-dien-3β-yl acetate (III). This chlorohydrin is produced by a reaction between equimolar amounts of the 5,8-peroxide (II) and the acetate (I), the generality and mechanism of which are discussed briefly.

Ionic ‘Diels–Alder’ reactions of hexa-3,5-dienyl trimethylsilyl ether and enones: X-ray structural determination of adduct stereostructure, and a stereoselective approach to trans-fused octalin systems

The trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBDMS) ethers of hexa-3,5-dien-1-ol react with cyclohexenones and an acyclic enone, methyl vinyl ketone (MVK), in the presence of 5–10 mol% of Me3SiOSO2CF3(TMSOTf) in MeCN to provide trans-fused adducts arising via ionic (Gassman-type) Diels–Alder reactions; structural confirmation for adduct stereochemistry for this type of reaction is provided by an X-ray structural determination.