RAMBERG-BACKLUND-PAQUETTE

PAQUETTE Olefin Synthesis OesuHonatlon of suHones to alkenes (altemative to Ramberg-Backlund). 

Cf. three-membered ring sulfones as intermediates of the Ramberg-Backlund reaction L. A. Paquette, Org. React., 25, 1 (1977). 

A review on the Ramberg-Backlund reaction has updated the Paquette review of 1977.45 Benzyl benzyl sulfone systems have been found to give unexpectedly high Z-stereoselectivity (up to E.Z = 1 16) in the Meyers variant of the Ramberg-Backlund (g reaction.46... 

It is now widely accepted that a-halo sulfones are converted into alkenes under the basic conditions of the Ramberg-Backlund reaction via intermediate thiirane 1,1-dioxides (Scheme 7). Experimental data in support of this mechanism were first put forward by Bordwell in 1951, and extensive studies carried out since that time, particularly by Bordwell and Paquette in the late 1960s and early 1970s, have substantiated this overall scheme and have provided further insight into the mechanisms of the individual steps. Very little additional work concerning the mechanism of the reaction has been published since 1975. Consequently, only a summary of the essential features is presented here, and readers are referred to the detailed reviews, written by the leaders of the key research groups themselves, for the full data which support the following broad outline. ... 

In spite of an unpromising early report,the Ramberg-Backlund rection has been applied with great success since the early 1970s to the synthesis of cyclobutenes, particularly by Paquette and Weinges. Al-... 

In 1964, Paquette reported that although the 9,10-double bond of simple phenanthrenes can be formed using the Ramberg-Backlund reaction (NaOH in aqueous dioxane), the sterically crowded 4,5-dimethyl-phenanthrene cannot be made by this method. Staab has now shown that the highly strained proton sponge 4,5-bis(dimethylamino)phenanthrene (15) can be prepared using Meyers modification of the re-... 

Conversion of dialkyl sulfones to alkenes either by rearrangement of a-halosulfones with base (via S02 elimination from thiaranedioxides) (Ramberg-Backlund) or by desulfonation of sulfones with BuLi-LAH(Paquette) (see 1st edition). 

Paquette was the first to make cyclobutenes by taking advantage of the Ramberg-Backlund reaction.30,31 Treatment of sulfone 38 with potassium r-butoxide led to cyclobutene 39 in 61% yield after distillation regardless of the configuration of the chlorine atom on the substrate (38). The ease with which cyclobutene ring formation occurred in this example was particularly noteworthy. In the same fashion, cyclobutene 42 was obtained from the Ramberg-Backlund reaction of either epimer 40 or 41.32... 

Early in his academic career in 1964, Paquette carried out the Ramberg-Backlund reaction of chloro-sulfone 65 to make phenanthrene 66.44 He discovered that conformational requirements of a-sulfonyl carbanion prolonged the reaction time (5 days) in some cases. In 1986, applying the Meyers modification, Staab et al. converted sulfone 67 to phenanthrene 68.45 The two chlorine atoms on 68 were the result of overchlorination where tetrachloro-sulfone was generated in situ. 

PAQUETTE Olefin Synthesis Desulfonation o( sutfones to alkenes (alternative to Ramberg-Backlund). 

Treatment of a-halosulfones 357 bearing a -hydrogens with base gives olefins by extruding SO2 from the episulfone intermediates 359. The reaction was found by Ramberg and Backlund in 1940 and named after them, and it has been very useful for the preparation of tailor-made olefins. The reaction has been investigated in detail " and utilized widely for olefin syntheses. An excellent review on this reaction by Paquett covers the literature up to 1975, so only recent studies are dealt with in this section. The generally accepted mechanistic path is shown below. 

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