Acetals from alkenes

The reaction takes place in the medium of acetic acid and yields are generally good. This is why the route to obtain aldehydes or ketones from alkenes via glycol formation is preferred over that of ozonolysis. Other compounds which are readily cleaved include those with the groups ... 

A second type of organopalladium intermediates are 7r-allyl complexes. These complexes can be obtained from Pd(II) salts and allylic acetates and other compounds with potential leaving groups in an allylic position.79 The same type of 7i-allyl complexes can be prepared from alkenes by reaction with PdCl2 or Pd(02CCF3)2.80 The reaction occurs by electrophilic attack on the n electrons followed by loss of a proton. The proton loss probably proceeds via an unstable species in which the hydrogen is bound to... 

Application of the oxymercuration-demercuration reaction176 to alkyl 3,4-dideoxy-a-DL-hex-3-enopyranosides provides177 easy access to alkyl 3-deoxyhexopyranosides (for example, 288). Interestingly, both stereoisomeric forms of the alkene are apparently attacked by mercuric acetate from the same side. It has been assumed177 that the transient, mercurinium ion 287 is stabilized by bonding to the 1-meth-oxyl group. 

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

An alternative route from alkenes to 2-azasulfides reported by the groups of Caserio and Trost involves addition of a thiosulfonium salt, e.g. dimethyl(methylthio)sulfonium tetrafluoroborate (MeSS-Me2+ BF4-), followed by treatment of the resultant thiosulfenylated adduct with an amine or other nitrogen nucleophiles (Schemes 2320 and 24).35 Trost reports that the addition of the thiosulfonium salt can be followed by addition of an oxygen nucleophile, such as acetate, or a carbon nucleophile, such as cyanide, effecting oxosulfenylation and cyanosulfenylation, respectively (Scheme 25).36... 

Considering the problem retrosynthetically, we can see that a key intermediate having the carbon skeleton of the desired product is 3-methyl-3-pentanol. This becomes apparent from the fact that alkanes may be prepared from alkenes, which in turn are available from alcohols. The desired alcohol may be prepared from reaction of an acetate ester with a Grignard reagent, ethylmagnesium bromide. 

The Woodward Reaction (or Woodward c/s-Hydroxylation) allows the synthesis of syn-diols from alkenes by the addition of iodine followed by nucleophilic displacement with acetate in the presence of water. Hydrolysis of the intermediate ester gives the desired diol. The Prevost Reaction gives crn/z -diols. 

In the second step meto-chloroperbenzoic acid (MCPBA) epoxidizes the resulting bis-acetal from the /J-face. The weak 0-0 bond of MCPBA undergoes attack by electron rich substrates like alkenes. This reaction is syn stereospecific and believed to take place via transition state 48.30... 

Acetal derivatives have been obtained from alkenes by 1,2-difunctionalization with IPy2BF4 followed by [l,2]-aryl or-alkyl group migration (Scheme 24)42... 

All reactions of Table 9.1 were performed in pyridine, usually at room temperature by addition of water, methanol, acetic acid, etc. it was possible to prepare several functionalized compounds from alkenes and alkadienes. 

The increased syn/anti selectivity observed in the Johnson-Claisen rearrangement of the ketene acetal from the trisubstituted alkene is an indication that the reaction goes through a six-membered chairlike transition state4 (Scheme 1.2d). Transition state B is disfavored compared to state A, due to the developing 1,3-diaxial interactions between the two methyl groups in the transition state. 

Both nltroaldol15 and t,3-dipolar cycloaddition products (e.g., isoxazolines, from alkenes)13 14 have shown that nitroacetaldehyde diethyl acetal 1 constitutes a versatile C2 building block in organic synthesis, notably what concerns amino sugar... 

Diphenyl carbonate from dimethyl carbonate and phenol Dibutyl phthalate from butanol and phthalic acid Ethyl acetate from ethanol and butyl acetate Recovery of acetic acid and methanol from methyl acetate by-product of vinyl acetate production Nylon 6,6 prepolymer from adipic acid and hexamethylenediamine MTBE from isobutene and methanol TAME from pentenes and methanol Separation of close boiling 3- and 4-picoline by complexation with organic acids Separation of close-boiling meta and para xylenes by formation of tert-butyl meta-xyxlene Cumene from propylene and benzene General process for the alkylation of aromatics with olefins Production of specific higher and lower alkenes from butenes... 

While enol acetates from saturated ketones were useful a-oxygenation substrates, the corresponding dienol acetates are not. The relatively electron-deficient alkene bearing the acetoxy group is less attractive h> elecm hilic oxygenating agents than the unsubstituted double bond. Thus, for example, peracid treatment leads to epoxidation the unfiinctionalized alkene.However, it would seem likely that re-... 

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