BURGESS Alcohol Dehydration

This chapter is concerned with a group of thermally induced elimination reactions widely used for the introduction of carbon-carbon double Irands into complex molecules. These reactions form a discrete group of elimination reactions in that they proceed with syn stereochemistry via concerted cyclic transition states. Related syn elimination processes are believed to be involved in other elimination reactions, e.g. alcohol dehydration using the Burgess reagent, but are not discussed here. One of the advantages of the syn elimination reactions discussed in this chapter is that they do not require the use of... 

Next, the TMS enol ether of 53c underwent oxidation with MCPBA to trimethylsilyloxy ketone 57. in 86% yield (86% conversion). Addition of methylmagnesium bromide in methylene chloride proceeded in almost quantitative yield (95%) to give tertiary alcohol 58. Dehydration with Burgess reagent [19] and acidic workup provided the allylic alcohol 59a in 63% yield, which was converted... 

Dehydrates secondary and tertiary alcohols to give olefins, but forms ethers with primary alcohols. Cf. Burgess dehydrating reagent. 

Burgess reagent, (methoxycarbonylsulfamoyl)triethylammonium hydroxide, usually used for the dehydration of secondary or tertiary alcohols, was successfully employed in the formation of cyclic sulfamidates from the corresponding epoxides. It was further shown that the same reaction with aromatic epoxides resulted in the formation of seven-membered ring systems, for example, 57 (Figure 23) <2003SL1247>. 

Fig. 4.29. Dehydration of an alcohol with the Burgess reagent (which in turn is prepared from 0=C=N-S02-CI by (1) addition of methanol and (2) reaction and subsequent deprotonation with triethy-lamine). The aminosulfuric acid ester intermediate decomposes via a cyclic transition state (syn-elimination).

Dehydration of 124 to the expected 1-seleno-l-vinylcyclopropanes was succesful only with tertiary alcohols of this type it required the use of thionyl chloride in the presence of triethylamine, pyridine or hexamethylphosphorus triamide followed by reaction with potassium t-butoxide in DMSO, or the use of the Burgess reagent... 

Fig. 4.25. Dehydration of an alcohol with the Burgess reagent. The aminosulfuric acid ester intermediate decomposes via a cyclic transition state (iyn-elimination).

Dehydration. Burgess et al. reported that the reagent is useful for dehydration of simple alcohols. The reaction is a stereospecific ds elimination and follows Saytzeflf s rule. Crabbe and Leon have used this procedure with various steroidal secondary and tertiary alcohols. They conclude that the nature of the alcohol group, the configuration, and the environment are the primary factors governing the course of dehydration. The reactions are carried out at room temperature in anhydrous benzene for 2 hr. followed... 

During the first total synthesis of taxol , R. Holton and co-workers installed an exo-methylene group on the C ring in order to set the stage for the D ring (oxetane) formation. The Burgess dehydration reaction was applied to a complex tricyclic tertiary alcohol intermediate (ABC rings) and the desired exocyclic alkene was isolated in 63% yield. 

Burgess dehydration Preparation of alkenes from 2° and 3° alcohols. 72... 

In one case the dehydration was most efficient using (methoxycarbonylsulfamoyl)triethylam-monium hydroxide, inner salt (Burgess reagent). This gave a 25% yield of 1-cyclopropyl-1-[1-(trimethylsilyl)cyclopropyl]ethene (11) from the corresponding tertiary alcohol 10. °... 

Elimination of methanesulfonate has been used in the synthesis of optically active dimethyl (5)-2-vinylcyclopropane-l,l-dicarboxylate (9). l,8-Diazabicyclo[5.4.0]undec-7-ene with a catalytic amount of 4-(dimethylamino)pyridine was used to effect elimination of the mesylate in nearly 50% yield. Other methods of obtaining vinylcyclopropane 9, including direct dehydration of the alcohol with the Burgess reagent, were unsuccessful. 

Burgess dehydrating reagent is efficient at generating olefins from secondary and tertiary alcohols. It does notwork with primary alcohols. 

Dehydration of tert-alcohols.2 This reaction can be effected with BF3 etherate (1-3 equiv.) in CH2CI2 at 25°. Yields are usually higher than those obtained with the Burgess reagent, thionyl chloride/amine, or p-tolucncsulfonic acid. When dehydration could result in two different alkencs, the more thermodynamically stable alkenc predominates. Noepcntyl tert-alcohols result in mixtures of alkencs, some resulting from a carbocation rearrangement. 

This is a mild and selective method of converting secondary and tertiary alcohols to their respective olefins by use of the stereospecific cw-dehydrating agent, methyl N-(triethylammoniumsulfonyl)carbamate (Burgess reagent, l).1... 

It has been mentioned earlier that when Burgess reagent is treated with primary alcohols the carbamate is formed rather than the dehydration product. The development of a benzyl Burgess reagent (49) was shown to convert primary alcohols to the corresponding amines that are conveniently protected with the Cbz group.15... 

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