Ramberg-Backlund rearrangement synthesis

Two illustrations that show the power of this reaction for the preparation of strained cycloalkenes are the contractions of 102 to the propellane 103 , an application that has been reviewed , and of 104 to the bicyclo[2.1.1]hexene 105 . The utility of the Ramberg-Backlund rearrangement in the preparation of various natural products such as steroids , terpenoids and pheromones has been demonstrated. In addition to the synthetic applications mentioned in the previous subsection, several selected examples taken from the recent literature are given in equations 66-69. These examples further demonstrate the potential of this method for alkene synthesis in general. 

Boekelheide and his collaborators [407] have described a two-step sequence for transforming sulfide linkages to carbon-carbon double bonds — Stevens rearrangement of sulfur ylides and Hofmann elimination — which they found particularly useful for the synthesis of cyclophane derivatives, such as the [2.2]metaparacyclophane-l,9-diene shown. The Ramberg-Backlund rearrangement (see Section 4.3.2) was unsatisfactory for such highly strained molecules. 

Cooke 17) has recently reported the synthesis of 18 in order to compare the steric interactions and rates of conformational flipping with other systems (2, 3, and 9). The synthesis of 18 has been accomplished in two ways, both involving the intermediate 2-thiapyridinophane one utilizes the Ramberg-Backlund rearrangement while the other depends on the Stevens rearrangement, as depicted in Scheme III. 

G. D. McAllister and R. J. K. Taylor, The synthesis of polyoxygenated, enantiopine cyclopentene derivatives using the Ramberg-Backlund rearrangement, Tetrahedron Lett., 42 (2001) 1197-1200. 

The fourth approach to the synthesis of manzamine C involved a Ramberg-Backlund rearrangement in the key step for the preparation of the azacycloundecene ring [81[. Synthesis ofthis ring began with thecondensationof5-amino-l-pentanol 156... 

The Ramberg-Backlund rearrangement was the key step in the total synthesis of the marine alkaloid manzamine C by D.l. MaGee and E.J. Beck. The azacycloundecene ring was stereoselectively formed by exposing the a-chloro sulfone to a strong base. The use of weaker bases either resulted in no reaction or gave rise to mixtures of ( )- and (Z)-alkenes. 

Internal alkylation takes place on reaction of a-haloalkyl alkyl sulfones with bases and produces epi-sulfones as intermediaries. These intermediates are usually unstable and provide alkenes by thermal extrusion of sulfur dioxide. This reaction, known as the Ramberg-Backlund rearrangement, has been widely used in synthesis and has been thoroughly reviewed (Scheme 107, entry e).36-3. 43<.473... 

Recent applications of the Ramberg-Backlund rearrangement to the synthesis of bioactive target molecules have been reviewed. Under Ramberg-Backlund conditions, exo-6-bromo-ryn-7-bromo(chloro)methylsulfonyl-enr/o-6-phenylbicyclo[3.1.11-heptane has been shown to yield flnft -6-hydroxy-7-methylene-iyn-6-phenylbicyclo-... 

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