Diols rearrangements

In the pinacol-pinacolone rearrangement a 1,2-diol rearranges to give a carbonyl group that is adjacent to a quaternary carbon. There are many variations of this reaction for example, the semipinacol rearrangement, in which a (P-amino alcohol is treated with nitrous acid. This reaction may be modified so that a ring expansion takes place, in which case it is called the Tiffeneu-Demyanov ring expansion. 

Diols rearrange in acid solution to give ketones—pinacol rearrangement. 

The ozonolysis of substituted-allyl silyl ethers or allyl esters followed by treatment with bases or Ph3P give the corresponding a-silyloxy ketones or a-acyloxy ketones.116 The reaction is proposed to proceed via an ene-diol rearrangement of the corresponding a-silyloxyaldehyde or a-acyloxyaldehydes intermediates. 

The rearrangement is also useful for furan aimulation, through enlargement of the starting carbocycle [82]. Thus addition of SnCU to either diastereomer of the allylic acetal produces the cw-fused cycloheptatetrahydrofuran in 48-76 % yield (Eq. 49). Acetals derived from frara-diols rearrange to the same cis-fused bicyclics in higher yield. 

Ring contractions of cyclobutane-1,2-diols have been widely reported. Both cis- and fran -cyclo-butane-l,2-diols rearrange under acid catalysis to give the corresponding cyclopropanecarb-aldehydes or ketones, generally in high yield. ... 

This rearrangement is general for i,2-diols of the type R2C(OH) C(OH) R2 where the groups R may be alike or different, and may be alkyl or aryl groups. 

The disconnection is obvious, and gives us one way of making symmetrical 1,2-diols. What makes it more than trivial is that the products undergo the pinacol rearrangement ... 

The base catalyzed rearrangement of a monotosylated 1,2-diol on alumina, followed by immediate condensation of the sensitive ketone with methylenetriphenylphosphorane, gave the exo-methylene compound below (G. Btlchi, 1966B). 

Thallium(III) acetate reacts with alkenes to give 1,2-diol derivatives (see p. 128) while thallium(III) nitrate leads mostly to rearranged carbonyl compounds via organothallium compounds (E.C. Taylor, 1970, 1976 R.J. Ouelette, 1973 W. Rotermund, 1975 R. Criegee, 1979). Very useful reactions in complex syntheses have been those with olefins and ketones (see p. 136) containing conjugated aromatic substituents, e.g. porphyrins (G. W. Kenner, 1973 K.M. Smith, 1975). 

An early attempt to hydroformylate butenediol using a cobalt carbonyl catalyst gave tetrahydro-2-furanmethanol (95), presumably by aHybc rearrangement to 3-butene-l,2-diol before hydroformylation. Later, hydroformylation of butenediol diacetate with a rhodium complex as catalyst gave the acetate of 3-formyl-3-buten-l-ol (96). Hydrogenation in such a system gave 2-methyl-1,4-butanediol (97). 

Principal terpene alcohol components of piae oils are a-terpiueol, y-terpiueol, P-terpiueol, a-fenchol, bomeol, terpiuen-l-ol, and terpiaen-4-ol. The ethers, 1,4- and 1,8-ciaeole, are also formed by cycli2ation of the p-v( enthane-1,4- and 1,8-diols. The bicycHc alcohols, a-fenchol [512-13-0] (61) and bomeol (62), are also formed by the Wagner-Meerweiu rearrangement of the piaanyl carbonium ion and subsequent hydration. Bomeol is i7(9-l,7,7-trimethylbicyclo[2.2.1]heptan-2-ol [507-70-0]. Many other components of piae oils are also found, depending on the source of the turpentine used and the method of production. 

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

The third approaeh to synthetic polymers is of somewhat less commereial importance. There is in fact no universally accepted deseription for the route but the terms rearrangement polymerisation and polyaddition are commonly used. In many respects this process is intermediate between addition and condensation polymerisations. As with the former teehnique there is no moleeule split out but the kinetics are akin to the latter. A typical example is the preparation of polyurethanes by interaction of diols (di-alcohols, glycols) with di-isocyanates Figure 2.7). 

The pinacol rearrangement is frequently observed when geminal diols react with acid. The stmcture of the products from unsymmetrical diols can be predicted on the basis of ease of carbocation formation. For example, l,l-diphenyl-2-metltyl-l,2-propanediol rearranges to... 

Antithetic conversion of a TGT by molecular rearrangement into a symmetrical precursor with the possibility for disconnection into two identical molecules. This case can be illustrated by the application of the Wittig rearrangement transform which converts 139 to 140 or the pinacol rearrangement transform which changes spiro ketone 141 into diol 142. 

Sometimes reduction of a ketone by NaBH4 is accompanied by hydrolysis of an ester elsewhere in the molecule. Norymberski found that a 20-keto-21-acetoxy compound with NaBH4 in methanol at 0° for 1 hour gives the 20/ ,21-diol. 50 % aqueous dimethylformamide has been used as the solvent in an attempt to prevent acetate hydrolysis, but sometimes under these conditions the 21-acetoxy group migrates to the 20-position. The rearrangement is favored by addition of the 20-acetate as seeds or by addition of... 

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). 

Chromatography of 3, 17jS-dihydroxypregn-5-en-20-one (82a) on alumina affords the rearranged product 3/ ,17a/ -dihydroxy-17aa-methyl-D-homo-androst-5-en-17-one (84a) in quantitative yield.On the other hand, treatment of diol (82a) or diacetate (82b) with methanolic potassium hydroxide... 

Base catalyzed pinacol rearrangement of vicinal m-glycol monotosylates is a simple and useful general method for preparing perhydroazulenes. Thus, treatment of cholestane-5a,6a-diol 6-tosylate (115a) with either one mole-equivalent of potassium t-butoxide in f-butanol at 25° or with calcium carbonate in dimethylformamide at 100° gives a quantitative yield of 10(5 6/5H)... 

A simple and direct approach to 10(5 4j H)<2Z)eo-5-lceto derivatives lacking functionality in ring A is the controlled pinacol rearrangement of vicinal cw-diols analogous to the process described in the previous section. An example is the reaction of cholestane-4a,5a-diol 4-tosylate (136) with 1 mole-equivalent of potassium t-butoxide or with dimethylforraamide-calcium carbonate at reflux which gives a quantitative yield of Q(5ApH)abeo-cholestan-5-one (137). ... 

A nonphotochemical method for the preparation of D-norsteroids involves the base-catalyzed pinacol rearrangement of a pregnane-16oc,17a-diol 16a-mesylate. ... 

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