2.3- Butanediol oxidative cleavage

It not tertiary, the product yield is lowered by transfer of the carbinol hydride ion to the aldehyde to produce a new alkoxide and an enolate ion. Thus, propylene oxide, after reductive cleavage with LDBB and trapping with isobutyraldehyde or p-anisaldehyde, provided 5-methyl-2,4-hexanediol in 40-50% yield or 1-p-anisyl-1,3-butanediol in 44% yield, respectively (in both cases about equal mixtures of diastereoisomers were obtained). The cyclohexene oxide-derived dianion, when trapped with isobutyraldehyde, gave 2-(1-hydroxy-2-methylpropyl)cyclohexanol in 71% yield as a mixture of only partially separable isomers in the ratio 15 11 39 35. 

Asymmetric induction in cyclizution of a dienic acetal. Johnson et al reported a very high degree of asymmetric induction in the SnCl4-catalyzed cyclization of the iiL ctal I, derived from (—)-2,3-butanediol. Cyclization results in two axial ethers and two equatorial ethers cleavage and Jones oxidation converts these products into an nctuionc mixture consisting of 2a and 2b in the ratio 8 92. 

Pentanediol is often superior to other diols such as 2,3-butanediol for these reactions because of higher distereoselectivities in reactions with nucleophiles and the more facile cleavage of the resulting hydroxy ether by oxidation-p-elimination. Removal of the chiral auxiliary is usually carried out with Pyri-dinium Chlorochromate oxidation followed by p-elimination using KOH, K2CO3, piperidinium acetate, dibenzylammonium trifluoroacetate, " or DBU. In some cases, 1,3-butanediol is preferred because the final 3-elimination may be effected under milder conditions. ... 

Table II shows results for the electro-oxidation of secondary alcohols and ketones. In alkaline electrolyte, secondary butanol was not oxidized to methyl ethyl ketone but was cleaved to acetate. Similarly methyl ethyl ketone was cleaved to acetate, although some CO2 and propionate formed, indicative of cleavage on the other side of the carbonyl group. Butanediol (2 ) went to acetate yielding less CO2. At pH 9 in borax buffer 2 Trtanol went exclusively to methyl ethyl ketone at 89% conversion, suggesting that enolization in alkali is a necessary part of the cleavage process. Cyclohexanol and cyclohexanone were both converted to adipic acid. Figure 12 summarizes the various types of electro-organic oxidations, thus far discussed, which are observed to occur on lead ruthenate in alkaline electrolyte.

The group of M. J. Kurth [36] used polymer-bound enones for the Michael-type addition of aryl thiolates (Fig. 6.20). In the first step 1,4-butanediol was attached to PS-tritylchloride resin. This was followed by an oxidation to the aldehyde, subsequent Wittig reaction and addition of aryl thiolates. Cleavage was performed with formic acid in THF. 

---