Unique Reactions of Diols

Using our knowledge of alcohol reactions, we can explain results that seem strange at first glance. The following dehydration is an example of the pinacol rearrangement  

Step 1 Protonation of a hydroxyl group. Step 2 Loss of water gives a carbocation. 

2-Diols (glycols), such as those formed by hydroxylation of alkenes, are cleaved by periodic acid (HIO4). The products are the same ketones and aldehydes that would be formed by ozonolysis-reduction of the alkene. Hydroxylation followed by periodic acid cleavage serves as a useful alternative to ozonolysis, and the periodate cleavage by itself is useful for determining the structures of sugars (Chapter 23). 

Periodic acid cleavage of a glycol probably involves a cyclic periodate intermediate like that shown here. 

Periodic acid cleaves a diol to give the same products as ozonolysis-reduction (O3 followed by Me2S) of the alkene. 

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Problem-Solving Strategy Proposing Reaction Mechanisms 491 11-11 Unique Reactions of Diols 494... 

More remarkably, the reaction forming the Mn-Pt species is unique among the compounds 144-149 in that three other metallacarborane products were also isolated from this system alone. These are two 12-vertex species, [l-Ph-2,2,2-(CO)3-7-X-8,8-dppe-/iyperc/oAo-8,2,l-PtMnCBgHg] pC = H (150), OEt (151)], and the complex [3,6,7- Mn(CO)3 -3,7-(p-H)2-l-Ph-6,6-dppe-c/oio-6,l-PtCBgH6] (152) formed by cluster contraction. Subsequent studies confirmed that the ethoxylated compound 151 is formed by reaction of 146 with adventitious EtOH present in the precursor 129. Indeed, treatment of 146 with other alcohols ROH afforded similar species [l-Ph-2,2,2-(CO)3-7-OR-8,8-dppe-/z3y crc/oA o-8,2,l-PtMnCBgHg] [R = Me (153), (CH2)20H (154), (CH2)40H (155)] with, surprisingly, only mono-cage products observed when diols were used as substrates. All of the alkoxy-substituted compounds 151 and 153-155 are relatively stable and do not react further, whereas... 

The scope and synthetic utility of dioxyphosphoranes, and particularly, diethoxytriphenylphosphorane (DTPP), as useful cy-clodehydrating "reagents" for the conversion of diols to cyclic ethers have received only superficial attention (1). The DTPP-diol - ether route has several unique advantages over existing methods (a) the reaction conditions are effectively neutral and mild, (b) the stereoselectivity in the closure of both unsymmet-rical and symmetrical diols to cyclic ethers is high, and (c) the isolation of the product(s) from triphenylphosphine oxide (TPPO) is convenient. 

Using a strategy similar to the asymmetric acylation described above (4.1.1), the symmetrical 2,5-dibenzoate 172 was transformed to the optically pure diol 174 in 70% yield with complete enantioselectivity by the reaction of one pair of the two enantiotopic vicinal diols with the novel chiral pyranyl pyran 173 with a C2 axis in the presence of camphorsul f onic acid (CSA) (Scheme 4-3). 72 This unique spiroketal, which is named dispoke... 

There has been no report on the reductive elimination of sulfate ester by thiols. Thus, the transformation of GTXs to STXs via the intermediate conjugates is considered to be quite a unique reaction. Formation of the conjugates does not occur under acidic conditions. Furthermore, it was confirmed that GTXs-12-ol, analogues in which the gem diol at C12 is reduced, did not react with thiols at all. These facts indicate that the characteristic keto-gem diol structure at C12 of the toxins is essential for the reaction [29], When the equilibrium mixture of a- and 3-0-sulfate toxins is incubated with thiols, the a-O-sulfate toxin is consumed faster than the P-O-sulfate toxin in the formation of the conjugates, showing that a-O-sulfate toxin is a reactive isomer [30],... 

This condensation polymer is unique insofar as it can be a coating and varnish, a soft or hard foam, a resilient or rigid elastomer (rubber) as well as an adhesive. It is prepared by the reaction of a diisocyanate (OCNRNCO) with a diol (HOR OH) where R can be an aromatic radical such as toluene (TDI-2,4, toluene diisocyanate). 

Second, 1,4-diols undergo intermolecular hydrogen transfer, giving lactones efficiently in acetone containing Cp Ru(P-N) catalysts the TOF of this reaction at 30 C exceeds 1,000 h (Fig. 21) [67]. The catalytic oxidative lactonization of diols is characterized by its unique chemo- and regioselectivity. The significant rate difference between primary and secondary alcohols in dehydrogenation, and the rate difference between 1,4-diols and 1,5- or 1,6-diols enable unique oxidative lactonization of triols. 

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