Wagner-Meerwein type 1,2 -rearrangement

The Bamford-Stevens decomposition of tosylhydrazones by base has been applied to steroids, although not extensively. It has been demonstrated that the reaction proceeds via a diazo compound which undergoes rapid decomposition. The course of this decomposition depends upon the conditions in proton-donating solvents the reaction has the characteristics of a process involving carbonium ions, and olefins are formed, often accompanied by Wagner-Meerwein-type rearrangement. In aprotic solvents the diazo compound appears to give carbene intermediates which form olefins and insertion products ... 

The predominantly syn stereochemistry of the products arising from the bicyclo[3.2.1] octyl cation IV would results from the large ring strain in II, the chair conformation of which, (but not boat) facilitate the Wagner-Meerwein type rearrangement. 

The presence of a quaternary atom, for instance, may be traced back to either a "pinacol" or a "Wagner-Meerwein-type" rearrangement. In the classical "pinacol rearrangement", pinacol 1 (a 1,2-diol) under strong acid conditions rearranges to pinacolone 2 which bears a quaternary atom at the a-position of the carbonyl group ... 

AuBr3(vp) reacts slowly (8 hours) with refluxing methanol or ethanol to form the chelate compounds AuBr2(vp OR) (R = Me, Et) shown in Fig. 25. A Wagner-Meerwein type rearrangement from a five- to a... 

Kneen showed that a Wagner-Meerwein type rearrangement occurred on reaction of AuBrs(vp) with methanol and ethanol, the substituted product having a 6-membered ring system. Ionisation, rapid rearrangement of the primary carbonium ion to a more stable secondary, benzylic carbonium ion and subsequent attack by solvent can account for this reaction. 

Wagner-Meerwein type rearrangements have also been widely reported in terpene chemistry [127, 128]. One well-known transformations involves the... 

Analogous reactions of 3-diazobicyclo[2.2.1]heptan-2-one with perchloric acid in alcohols, such as ethanol, gave the corresponding ethers, e rfo-3-ethoxybicyclo[2.2.1]heptan-2-one (34%),, n -2-ethoxybicyclo[3.1,1]hcptan-6-onc (41%) and methyl cyclohex-3-enecarboxylate.69 Further examples of the formation of cyclobutanes from cyclopentanes via Wagner-Meerwein-type rearrangements are given in Table 2. 

Table 2. Wagner-Meerwein-Type Rearrangements of Cyclopenlanes to Cyclobulanes...

Mention should be made of the 9-phenylhomocub-l(9)-ene (5) to l-phenylhomocub-9-ylidene (6) rearrangement, which is believed to result from a Wagner-Meerwein-type rearrangement of the zwitterionic state of the alkene.3,4... 

A radical-based Wagner-Meerwein-type rearrangement has been reported where the radical was generated from the epoxide using CP2T1CI as the radical source.163... 

M. Nakazaki, Mechanism of Plancher s rearrangement. II. Twofold Wagner-Meerwein-type rearrangement of indolenium compounds, Bull. Chem. Soc. Jpn. 33, 472-475 (1960). 

During the acid catalyzed esterification of dicyclopentadiene 47, a rapid Wagner-Meerwein type rearrangement occurs simultaneously, according to the reaction scheme 2 (Eq. 15.5.2). The ester compound contains exclusively the dicyclopentenyl component in the exo-form. 

A Wagner-Meerwein-type rearrangement of the cation has been often observed in the oxidation of carboxylic acids (equation 59). The relative migratory aptitude of R and R has been studied, and this type of rearrangement has been applied to the synthesis of )-muscone (equation 60). ... 

Examples of Wagner-Meerwein-type rearrangements are found in simpler systems, such as neopentyl chloride (example a) and even 1 -bromopropane (example b). These two examples illustrate the following points ... 

Details have appeared of the synthesis91 and rearrangement92 of 3a,4a- and 3p,4p-epoxy-D A-friedo-18p,19a-H-lupanes (seeVol. 11, p. 123). Wagner-Meerwein type rearrangements of some lupane derivatives have been studied.93 The 13C n.m.r. spectra of some lupanes have been reported.94... 

In unsaturated hydrocarbon systems where Wagner-Meerwein-type rearrangements, transannular hydrogen shifts or transannular rc-participations are possible, such reactions do occur.8 Moreover, in the bromofluorination of 9-oxabicyclo[6.1.0]non-4-ene, a transannular reaction involving oxygen participation has been observed.9... 

These results indicated that the Wagner-Meerwein-type rearrangement was followed by a stereospecific hydride transfer from C-18a to C-13a which led to an immonium ion, the latter finally being reduced to derivative (11) (Scheme 1). Inversion at position 12, as expected for a Wagner-Meerwein-type rearrangement, is in accordance with the generality of the c-nor-D-homo rearrangement. 

The one-carbon atom ring expansion of the myriad cyclohexane precursors is obviously one of the preferred methods available. There are two general approaches, involving cyclopropanation of a cyclohexene followed by cleavage of the intercychc C—C bond, or nucleophilic addition and Wagner-Meerwein-type rearrangement, as shown in Fig. 9. 

When trisubstituted olefins (R H) were employed as substrates in the same sequence, the intermediary indoles could undergo a Wagner—Meerwein type rearrangement to afford 2,3-disubstituted indoles (Scheme 5.151) [43]. The migration tendency of the groups is dependent on the nature of the substituents, as depicted in the scheme. 

Scheme 5.151 Tandem hydroformylation-(Fischer indolization)-(Wagner-Meerwein-type rearrangement) reaction.

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