Dienes acetoxylation

Pd-hydroquinone-mediated electrochemical 1,4-diacetoxylation of cyclohexa-1,3-diene (118), leading to 1,4-diacetoxycyclo-hex-2-ene (119), has been investigated (Scheme 46) [156]. Palladium-catalyzed indirect electrochemical monoacetoxylation of olefins has been attained in an MeCN/Ac0H-NaC104/Ac0Na/Pd(0Ac)2-Cu(OAc)2-(C) system. The acetoxylation of cyclohexene produces unsaturated esters with less current efficiency, giving a 1 1 mixture of allylic and vinylic products [118]. 

Alkenes can be transformed to carbonyl compounds through the oxidation of the vinylic carbon atom. A special case of vinylic oxidation is acetoxylation of alkenes and dienes. 

Acetoxylation of Alkenes, Dienes and Aromatic Hydrocarbons 61.3.4.3.1 Vinyl acetate from ethytene... 

The Co(f-butylsalophen) complex entrapped in zeolite Y was shown to be an essential member of electron chains designed for alcohol oxidation11301 and for the acetoxylation of 1,3-dienes with dioxygen.1131 1321 The Co(f-butylsalophen)Y... 

An earlier report [i8y] of the formation of 4a-acetoxy-cholest"5"en-3 One (4) from cholest-5-en-3-one (3) can now be interpreted as a preferential a-face attack upon the enolic 3,5-diene. The stereochemistry of acetoxylation suggests a connection with the sterically-controlled 4 -deprotonation of the A -3-ketone discussed in Chapter 4, section 6, but electrophilic attack at C<4) rather than at C 6> in the neutral enol is abnormal, and probably indicates that acetoxy transfer occurs via a cyclic transition state (3 with the reagent bonded to the C(3)-oxygen substituent. Corey [188] has proposed a mechanism of this type, and suggested that the enol triacetoxy-plumbate cf. 5) may arise by direct reaction between the ketone and the reagent. Supporting such an interpretation, the 3-acetoxy 3,5 diene(6) reacted normally (p. 184) with lead tetraacetate to give the 6j -acetoxy-A -3-ketone 7) [i8g] instead of a 4-acetoxy derivative. 

Stereoselective Cyclizations. Sultams have been demonstrated to be superior sources of chirality in selected cases of iodolactonizations, oxidative 1,5-diene cyclizations, and Claisen-type rearrangements of p-acetoxyl substrates. ... 

The anodic dimethoxylation of simple cyclic olefins, such as cyclohexenes, results in the predominant formation of ra/w-dimethoxycyclohexanes [303,305]. However, Barba and CO workers [306] reported that the stereochemistry of l,2-dimethoxy-l,2-dihydroace-naphthene derived from acenaphthene is drastically influenced by the anode material. Palasz and Utley [307] have reported that jV-acetylpiperidines are methoxylated via the enamide intermediate species formed by the oxidation. 1,3-Dienes are also 1,4-dimethoxylated in low stereoselectivity [293]. The anodic methoxylation of or-pinene proceeds similarly to the acetoxylation, resulting in the formation of two sets of stereoisomeric products [308]. 

An improved route to aldosterone makes use of the 1 IjS-nitrite of a l,4-dien-3-one derivative (415), where C-19 is tilted away from the lljS-oxygen atom, to achieve attack (Barton reaction) only at C-18. The subsequent steps include some unusual heterocyclic chemistry. The 18-oxime (416) cyclized on heating to give the nitrone (417), thereby affording the necessary activation for acetoxylation at C-21. 

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