Wagner-Meerwein type

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 ... 

In spite of the known tendency of norbornene and related systems to undergo rearrangements of the Wagner-Meerwein type during eleetro-philic addition, no such rearrangement was observed when norbornene underwent cycloaddition with the acridizinium or the. A/ -methylenium benzamide cation. As Schmidt correctly pointed out, this lack of rearrangement is an argument for a concerted reaction. Alternatively, if the cycloaddition is nonsynchronous, the time interval between step 1 and step 2 must be very short. 

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... 

Reimann et al.17 visualize this transformation as a formal example of a Wagner- Meerwein type of radical rearrangement. The mechanism suggested by these works is outlined in structures 65 to 68. The inter-... 

The formation of sesquiterpenes by a carbocation mechanism means that there is considerable scope for rearrangements of the Wagner-Meerwein type. So far, only occasional hydride migrations have been invoked in rationalizing the examples considered. Obviously, fundamental skeletal rearrangements will broaden the range of natural sesquiterpenes even further. That such processes do occur has been proven beyond doubt by appropriate labelling experiments, and... 

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 ... 

Prilezhaeva, E. N. Thiyiation of multiple bonds. Wagner-Meerwein type of rearrangement of sulfur- and chlorine-containing norbornenyl radicals. Organosulfur Chem. 1967, 57-74. 

Greci, L., Carloni, P., Stipa, P. Acid catalyzed rearrangements on indole systems. Wagner-Meerwein type transpositions. Topics in Heterocyclic Systems Synthesis, Reactions and Properties 1996, 1, 53-61. 

Since its discovery in the context of the reactions of the monoterpenoids, examples of the rearrangement have been found in many other systems. Therefore, for the purposes of this chapter, which is concerned with the synthetic utility of the Wagner-Meerwein type of rearrangement, some reactions involving substituents migrating will be included as well as examples of skeletal rearrangement in polycyclic systems. 

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... 

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