Allyl alcohol formation

Optimum conditions for allylic alcohol formation ( 65% yield of olefin mixture) appear to be those originally described by Wharton, rather than strongly basic forcing conditions. The pyrazole (147) is a by-product. 

Recent work, focused on some mechanistic aspects of this reaction, revisited the fundamental allylic alcohol formation reaction.181 Pyridine easily replaced DME of 118 to give bis(pyridine) complex 120 (Scheme 51). 

Two examples using i-BuLi/(—)-sparteine mixture as base have been reported to promote effective allylic alcohols formation in moderate ee for the spiro epoxide 82 and cyclooctadiene oxide 83 ° (Scheme 33). In the last case, such regioselectivity could be explained by the relatively flat conformation of the medium-sized oxirane which favors the syn base-oxirane complex (see Section n.A). 

The striking differences observed for the reaction of NBS with allyl alcohol vs crotyl alcohol have been rationalized as follows with allyl alcohol, formation of the solvated bromonium ion and HOBr are rate-limiting steps. By contrast, with crotyl alcohol, the rate-limiting step appears to be the breakdown of an NBS-crotyl alcohol complex, formed in a fast pre-equilibrium178. 

It is possible to write a cyclic destannylation mechanism for allyl alcohol formation as shown in Scheme 3, but this implies hydroxylation syn to the departing tin group, and there is evidence that this concerted route (2) is not dominant (Scheme 3). ... 

Sharpless asymmetric epoxidation ° is an enantioselective epoxidation of an allylic alcohol with ferf-butyl hydroperoxide (f-BuOOH), titanium tetraisopropoxide [Ti(0-fPr)4] and (-b)- or (—)-diethyl tartrate [(-b)- or (—)-DET] to produce optically active epoxide from achiral allylic alcohol. The reaction is diastereoselective for a-substituted allylic alcohols. Formation of chiral epoxides is an important step in the synthesis of natural products because epoxides can be easily converted into diols and ethers. 

Table 2 Comparison of Selective Reagents for Allylic Alcohol Formation over Saturated Ketone or Alcohol in...

Epoxidation of acyclic allyl alcohols with peracid and Mo/TBHP displays an opposite stereospecificity to that for the V/TBHP system. Trimethylsilyl-substituted allylic alcohols give t/zreo-epoxyalcohols with MCPBA and erythro-alcohols with VO(acac)a-TBHP, with high stereoselectivity. In the stereospecific epoxidation of cis- and trans-allyl alcohols, formation of a transition state is assumed with the development of two H bonds between the hydrogen atom of the hydroxy group of the allyl alcohol and the oxygen of the peracid, and between the hydrogen of the peracid OH and the oxygen of the ether 10. An analysis of the diastereometric transition-state interactions for stereoselective epoxidation of acyclic allylic alcohols has been published. A conformational effect may be responsible for the unexpected cis major product in Eq. 2. 

Synonyms Formic acid 2-Propenyl ester Formic acid Allyl ester Allyl alcohol Formate... 

Electrophilic activation of allylic alcohols. Formation of lithium allyloxy-triphenylborates enables the Pd(0)-catalyzed substitution of allyl alcohols with soft nucleophiles such as malonate ester enolates. 

SCHEME 1. Mechanism of allyl alcohol formation by Se02 oxidation. 

EO/PO copolymers are synthesized at 120-180 C, 2-6 bar in s ibatch reactors where pnre alkylene oxide or a mixture of them is fed over time. Lower temperatures are used when PO is fed to limit the intervention of secondary reactions such as the hydroxyl dehydration [8] and allyl alcohol formation [9]. 

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