281. The C–H stretching bands of methoxyl groups

109

Hydrolysis of dioxolenium (acyloxonium) ions fused to anchored six-membered rings gives almost exclusively that hydroxyester in which the ester function is axial (and the hydroxyl group equatorial). With the exception of the orthoformate, a group of related orthoesters reacted similarly. The potential utility of these observations in stereoselective synthesis is suggested by the following examples. (a) With trans-decalin-cis-2,3-diol (21) formation of the mono-benzoate via the orthoester leads to the axial ester (23d) in good yield; this procedure is complementary to reaction with benzoyl chloride and pyridine, which gives the equatorial ester (24d) as the only isolated product. (b) The action of silver acetate and iodine in wet acetic acid (the Woodward-Prkvost reaction) on trans-A'-octalin gives the axial acetateequatorial alcohol (236) again as the only significant product. The generality of this stereoselectivity is further supported by a number of individual examples drawn from the chemistry of carbohydrates. A rationalization is offered which qualitatively accounts for the observed stereoselectivity and its absence in the hydrolysis of the orthoformate, and which is based on the differences in steric strain among the possible transition states that fulfil the stereoelectronic requirements of dialkoxycarbonium ion formation.

Section: Alkalirie Hydrolyses Of Hydroxyanisatesmentioning

confidence: 99%

Remarkable stereoselectivity in the hydrolysis of dioxolenium ions and orthoesters fused to anchored six-membered rings

King¹,

Allbutt²

1970

109

“…Treatment with tetraethylammonium bromide gave the expected mixture of the diaxial and diequatorial bromohydrin anisates; the relative amounts of the two isomers is, of course, the subject of prime interest of this account andis discussed more fully below. Reaction of 7 with dilute acetic acid, which was virtually instantaneous, gave a half ester which on alkaline hydrolysis gave the known glycol 5u-cholestan-2crY3u-diol (12). Of the two possible half esters, that in which the anisoxyl group is axial was formed in much greater amount, this remarkable stereoselectivity has already been reported in a brief communication (I 3), and will be discussed more fully in a subsequent publication.…”

Section: Synthesis and Proof Of Structure Of The Dioxolenium Ionsmentioning

confidence: 55%

Stereochemistry of bimolecular nucleophilic opening of a dioxolenium ring fused to an anchored cyclohexane system

King¹,

Allbutt²

1969

This paper describes the characterization of certain dioxolenium salts in which the heterocyclic ring is fused (via positions4 and -5) to an anchored cyclohexane ring, and the steric course of their bimolecular cleavage with nucleophilic reagents. It was found that diaxial opening is normally favored strongly over diequatorial; this is accounted for in terms of differences in angle strain in the transition states. The presence of a n axial (angular) methyl group gave a preference for diequatorial opening; on the other hand an analogous investigation of the diaxial : diequatorial opening ratio with epoxides showed the stereochemistry of the reaction to be virtually insensitive to an angular methyl group. These observations are interpreted in terms of the different non-bonded interactions arising from the different geometrical arrangements of epoxides and dioxolenium ions. The variation in the diaxial : diequatorial opening ratio is shown to be of significance in the interpretation of rates of diaxial -> diequatorial rearrangement.

“…'The syrup remaining on cvaporation of the ether, after dissolution in petroleutn ether, afforded crystals of triphenylmcthanc, but only intractable gums were obtained on evaporation of the mother liquors. However, the presence of methox)-triphenylmethane in the gum was s h o w~l b y an infrared peak of medium intensity a t 2825 cm-'characteristic of the methoxyl group (18) and found in an authentic specimen of methoxy-triphenylmethanc prepared by the method of Straus and Hiissy (19). The gum also showed a peak a t 2880 cm-I corresponding t o the C-H stretching vibration of triphenylmethane (20).…”

Section: General Procedz~rementioning

confidence: 99%

Organic Peroxides: Iii. Reactions of Dialkyl Peroxides With Organolithium and Organomagnesium Compounds

Baramki¹,

Chang²,

Edward³

1962

Optinlum conditions for obtaining arylall;yl ethers from the reactions of aryl-lithium or -magnesium cornpot~nds with dialkyl peroxides have been investigated. The reactions arc considered to take place by ionic or four-center mechanis~ns.Gil~nan and Adams (I) found that, while di-(triphenylmethyl) peroxide is inert to phenylinagnesiulll bromide, diethyl peroxide reacts with it to give a 34% yield of phenetole. Di-t-butyl peroxide does not react with this Grignard reagent (2), even a t 80' (3), but reacts a t ordinary temperatures with the less-hindered Grignard reagents derived from primary and secondary bromides to give low yields of t-butyl ethers.Because of the possible usefulness of this method for synthesizing certain otherwise inaccessible ethers, we have studied the reactions of four dialkyl peroxides with phenyllithium and the pheilyl Grignard reagent (Table I), as well as the reactioil of dirnethyl peroxide with some other organo-lithiunl and -1nagnesiunl coinpounds (