Rearrangement, vinylogous

Wagner-Meerwein rearrangement, double 29, 686 Wagner rearrangement, vinylogous 29,987 Water (s. a. imder Potassium ter -butoxide)... 

The photochemical rearrangement of enamides to vinylogous amides was described (65],652). Rearrangement of cyclopropyl ketimines to enamines with acid was applied to syntheses of myosamine, apoferrosamine, mesembrine, and desmethoxymesembrine (653-656). 

A related enamine alkylation is seen in the rearrangement of an ethylene imine vinylogous amide, which was heated with sodium iodide in diglyme. The presumed internal enamine alkylation constitutes a critical step in an oxocrinane synthesis (265). Use of an ethylene imine urethane for alkylation of an enamine and formation of the hexahydroindole system has also been reported (266). 

Rearrangements of vinylogous urethanes to vinylogous carbonic acids and decarboxylation are other interesting enamine rearrangements which may be synthetically useful in the formation of cyclic enamines (623,624). 

The interesting aspect of this oxidation is that it is a vinylogous a-hydroxylation, and it offers the possibility that the following rearrangement could occur. 

Products of a so-called vinylogous Wolff rearrangement (see Sect. 9) rather than products of intramolecular cyclopropanation are generally obtained from P,y-unsaturated diazoketones I93), the formation of tricyclo[2,1.0.02 5]pentan-3-ones from 2-diazo-l-(cyclopropene-3-yl)-l-ethanones being a notable exception (see Table 10 and reference 12)). The use of Cu(OTf), does not change this situation for diazoketone 185 in the presence of an alcoholl93). With Cu(OTf)2 in nitromethane, on the other hand, A3-hydrinden-2-one 186 is formed 160). As 186 also results from the BF3 Et20-catalyzed reaction in similar yield, proton catalysis in the Cu(OTf)2-catalyzed reaction cannot be excluded, but electrophilic attack of the metal carbene on the double bond (Scheme 26) is also possible. That Rh2(OAc)4 is less efficient for the production of 186, would support the latter explanation, as the rhodium carbenes rank as less electrophilic than copper carbenes. 

Metal-catalyzed decomposition of p,y-unsaturated a -diazoketones 400 in the presence of an alcohol affords rearranged y,8-unsaturated esters 407 this process has been termed the vinylogous Wolff rearrangement193 . Full accounts dealing with the... 

The intramolecular addition of alkynyl-substituted a-diazoketones is catalyzed by Rh2(OAc)4 to give transient cyclopropenes, which spontaneously rearrange to vinylogous a-keto carbene intermediates for further carbon-skeleton transformations [54]. 

The reaction of a-halosulphonc with a base to give an olefin is known as Ramberg-Backlund reaction52. A vinylogous version of this rearrangement results in the formation of 1,3-dienes (equation 21)53. Another variation of this reaction is shown in equation 2254. These rearrangements proceed with moderate stereoselectivity. 

The ester/alkyne rearrangement system can be extended by conjugation to involve a more distant site. The reaction of diethyl phosphorochloridate with 3-methylhex-4-yne-2-ene-l-ol leads to the vinylogous propargylic ester rearrangement as shown in Equation 4.39.176... 

Interesting rearrangements proceed upon refluxing the azido diene 105 in benzene solution and form 61% of the vinylaziridine 106 as a mixture of diastereoisomers and the vinylogous urethane 108 (28%) (equation 37)53. It was shown that the process 106 - 108 occurs entirely at elevated temperature (refluxing xylene, ca 140 °C). However, treatment of the aziridine 106 with p-toluenesulfonic acid in THF at room temperature gives rise to trans,trans-, 3-butadiene carboxylic ester 107 in 98%53. 

A quantitative solid-state ene addition between two ligands of the platinum complex 397 gives the rearranged platinum complex 398 upon extensive heating to 140 °C [123]. This rearrangement reaction (cf. Sect. 24) is treated here, as it is the only known quantitative solid-state ene addition to date. Further quantitative solid-state [4-1-4] additions and higher vinylogs, as well as ene additions also of the intermolecular type, await detection both as thermal and photochemical reactions. 

Polysubstituted 2- or 5-methylpyrroles can be laterally chlorinated through a two-stage process that involves initial i/wo-chlorination in the )3-position, followed by rearrangement into the side chain. Migration is also possible from the vinylogous a -position (80JA1377). 

Rearrangement of vinylogous urethanes to give cyclic enamines [193, 194]. 

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