Diols, acid catalyzed rearrangements

Acid-catalyzed rearrangement of vicinyl diols (pinacols) to carbonyl compounds. 

The key step in the total synthesis of ( )-descarboxyquadrone was the hydrochloric acid catalyzed rearrangement of ll-acetoxytricyclo[4.3.2.0]undecan-2-one in refluxing diethyl ether to give 6-chlorotricyclo[4.3.2.01,5]undecane-5,10-diol (1) in 72% yield.16... 

Many carbonyl compounds can be synthesized by acid-catalyzed rearrangements of 1,2-diols (a type of reaction often called the pinacol-pinacolone rearrangement). 

In the course of a total synthesis of resiniferatoxin, an unexpected ring extension occurred, when 1,3-dioxane 236a was treated with an acid in chloroform. The ring extension was confirmed by acid-catalyzed rearrangement of diol 236b into dioxepane 237 (Scheme 70) <20040L4371>. 

The 1,8-terpins 9 and 10, which are monoterpenes of high flavor threshold, were observed in the acid hydrolysates of each variety. These diols are derivable as thermodynamically stable end-products of acid catalyzed rearrangement of monoterpenes v iich are at the oxidation state of geraniol. However, few conpounds at this oxidation state were seen among the aglycons, and the precursors of the terpins 9 and 10 in these varieties have yet to be discovered. 

Corey prepared the (6E,10Z)-LTB4 (115) from the previously described epoxy alcohol LTB4 synthon 119. Acid-catalyzed rearrangement of the derived phenylcarbonate 120 followed by protection, reductive cleavage of the vicinal carbonate, and cleavage of the resulting diol gave (2E)-r-butyldimethylsilyloxy-... 

Acid-catalyzed rearrangement of vicinal diols to aldehydes or ketones ... 

F I T T I G Pinacolone Rearrangement Acid catalyzed cartxjcation reanangement o< f, 2-diols to ketones... 

Selective hydroxylation with osmium tetroxide (one equivalent in ether-pyridine at 0 ) converts (27) to a solid mixture of stereoisomeric diols (28a) which can be converted to the corresponding secondary monotoluene-sulfonate (28b) by treatment with /7-toluenesulfonyl chloride in methylene dichloride-pyridine and then by pinacol rearrangement in tetrahydrofuran-lithium perchlorate -calcium carbonate into the unconjugated cyclohepte-none (29) in 41-48 % over-all yield from (27). Mild acid-catalyzed hydrolysis of the ketal-ketone (29) removes the ketal more drastic conditions by heating at 100° in 2 hydrochloric acid for 24 hr gives the conjugated diketone (30). 

A reaction that follows this pattern is the acid-catalyzed conversion of diols to ketones, which is known as the pinacol rearrangement.60 The classic example of this reaction is the conversion of 2,3-dimethylbutane-2,3-diol(pinacol) to methyl /-butyl ketone (pinacolone).61... 

Attempted peroxy acid epoxidation of the bicyclic ketone (31 equation 13) gave the lactone (33), instead of several possible rational alternatives. The epoxide (32) was implicated as an intermediate when it was independently synthesized from the epoxy alcohol, and shown to give (33) on treatment with aqueous acid.- A mechanism involving scission of the acyl bridgehead bond via the hydrated 1,1 -diol form of the ketone was proposed to account for the formation of this unexpected product. The rearrangement of the isolongifolene derivative (34 equation 14) appears to be mechanistically related. The product (35) is formed by brief treatment with dilute HCIO4 in dioxane as a mixture of isomers believed to arise by acid-catalyzed epimerization of the carbinol center. ... 

The pH-independent reaction of cyclopentadiene oxide 12 in water is clearly different from that of 13.97 This reaction yields 33% of 3-cyclopentenone, 35% of cis-2,4-pentadienal and 35% of a mixture of cis and trans 1,2- and 1,4-diols (Scheme 28). When the reaction is carried out in D20 instead of H20, no deuterium is incorporated into the ketone product. Thus, 1,2-hydrogen migration is required for this reaction just as it is in the rearrangement of arene oxides to phenols. The mechanisms of product formation in this reaction are not fully understood. The observation that the diol mixture is similar to that from the acid-catalyzed hydrolysis of 12 suggests that an allylic carbocation may be involved in the diol-forming reaction. Ketone (96) and dienal (97) products are potentially formed either by stepwise or concerted mechanisms, and there is insufficient evidence to rule out either one. There is a significant normal salt effect on this pH-independent... 

An nnnsnal ring-contraction reaction occnrs on the acid-catalyzed interaction of trimeth-ylhydroqninone 144 with cycloalkane-1,2-diols (e.g. 145) to form the spiro componnds 146 (eqnation 67) . Besides two isomers of cyclohexane-1,2-diols 145, this rearrangement was also described for cyclopentane-, cycloheptane- and cyclooctane-1,2-diols . 

The idea of solid-phase acid-catalyzed processes was originally developed by Toda et al. [46,47]. The pinacol rearrangement of aryl-substituted secondary and tertiary diols in the presence of solid p-toluenesulfonic acid (333 K) and trichloroacetic acid (293 K) was found to proceed faster and more selectively than in solution (batch reactor) [46]. 

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