Sulfonate esters lateral

Heliannuols are not an exception. Only one year later following the publication of heliannuol A, the first total synthesis of the racemic (+)-heliannuol A using the coumarin 18 as starting material was published.7 A key step in this synthesis was the ring closure achieved by two different methods intramolecular Julia coupling of the sulfone 19 and sulfone ester cyclization of the alternative sulfone 20 (Fig. 5.4.A). Desulfonation and demethylation yielded the desired (+)-heliannuol A. 

In general, on reaction with lithium aluminum hydride, secondary sulfonic esters are desulfonylated, with formation of the corresponding secondary alcohol. An exception is provided in an observation by Reist and coworkers, who treated 6-0-benzoyl-l,2-0-isopropyli-dene-5-O-p-tolylsulfonyl-a-D-glucofuranose, with lithium aluminum hydride in ether and obtained a product thought to be 6-deoxy-l,2-0-isopropylidene-y3-L-idofuranose, derived from an intermediate 5,6-anhydro-L-ido derivative later, Ryan and coworkers showed, from its nuclear magnetic resonance spectrum, that the product was 5-deoxy-l,2-0-isopropylidene-a-D- t/Zo-hexofuranose. The problem has been re-examined by Overend and coworkers the repetition experiment under the conditions of Reist and coworkers afforded 5-deoxy-... 

It is not essential to the theory to assume that a carbonium cation is actually liberated. Indeed, as we shall see later, it would be incorrect to do so. The essential point is that scission takes place between the ester oxygen and the alcohol carbon in sulfonic esters but not in carboxylic esters. 

A few years later the Swem laboratory then developed an activator which they claimed to be the most successful in activating dimethyl sulfoxide toward oxidation, namely, oxalyl chloride. Since oxalyl chloride reacted violently and exothermically with dimethyl sulfoxide, successful activation required the use of low temperatures to form the initial intermediate.6 Swem et al. reported the oxidation of long chain primary alcohols to aldehydes which was previously unsuccessful by first converting to the sulfonate ester (either mesylate or tosylate) and then employing the dimethyl sulfoxide-acetic anhydride procedure. They found that long-chain saturated, unsaturated, acetylenic and steroidal alcohols could all be oxidised with dimethyl sulfoxide-oxalyl chloride in high yields under mild conditions. 

In both SnI and Sn2 reactions, the leaving group is the halogen of an alkyl halide or the sulfonate group of a sulfonate ester. Both alkyl halides and sulfonate esters are prepared from alcohols. In Chapter 10, alcohols were prepared by the hydration reaction of alkenes, by oxymercuration-demercuration of alk-enes, or by hydroboration of alkenes. Other methods can be used to prepare alcohols, and they will be discussed at a later time. This section will describe several of the reactions used to convert alcohols to halides or sulfonate esters. 

This catalytic system tolerates terminal alkynes bearing various functionalities such as ketone, sulfone, ester, ketal, ether, alcohol, imide, or nitrile, which are useful for further transformations. The reaction with ethynyltrimethylsilane allowed the formation of the expected [6-1-2] cycloadduct in 92% yield. Such a result could not be obtained with the use of [(CHT)Co(CO)3] as catalyst [41]. Later, Hilt expanded the scope of the [6-t-2] cycloaddition to internal alkynes with modified pre-catalysts such as CoBr2[P(0/Pr)3]2 [55]. 

Recent synthetic applications of the photochemical [2 + 2] cycloaddition of unsaturated sulfones have been noted. Musser and Fuchs84 have effected an intramolecular [2 + 2] addition of a 6-membered ring vinyl sulfone and a five-membered ring vinylogous ester in excellent yield, as part of a synthetic approach to the synthesis of the mould metabolite, cytochalasin C. The stereospecificity of the addition was only moderate, however, and later problems with this synthetic approach led to its abandonment. Williams and coworkers85 have used the facile [2 + 2] photoaddition of 73 and... 

Remarkably, ethyl otolylsulfonate 456 can be laterally lithiated by BuLi at -78 °C 410 With the methyl ester, the expected substitution at the methyl group takes place. The -substituted ester also undergoes lithiation at the methyl group, suggesting that the sulfonate group acts substantially by conjugation. 

The selectivity of the radical relay chlorination is striking. In the case of the enone (13 Sdieme 18), and in related compounds with A-ring dienones, the m-iodobenzoate template at C-17 directs chlorination to C-9 and not to die preexisting functional groups of (13). The selective chlorination of C-9 seems to be quantitative, although in the first report the A "Lalkene (14) was isolated in only 77% yield. Later work has shown that the overall introduction of this double bond can have yields in the 90-93% range, and good yields for this reaction have also been reported from another laboratory. Template-directed radical relay chlorination on the a-face of steroids has also been successful in the a/b cu-coprostanol steroid series,and in the cholestanol series with iodophenyl templates linked by amide, ether, or sulfonate functions rather than carboxylic esters. ... 

Obrecht described the reaction of resin-bound thiouronium salt 111 vrith oxophe-nylbutynoic acid tert-butyl ester. Cleavage from the support was effected by S-oxidation to the sulfone followed by displacement vrith an amine [132]. The thiouronium salt pathway is illustrated in Scheme 26. Later, Masquelin et al. developed a condensation of resin-bound thiouronium salts with methylenemalononitriles to provide polymer-bound alkylthiopyrimidines 110 [133]. Pyrimidine derivatives 112... 

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