Phosphonium salts rearrangement

One of the most useful reactions in forming a P—C bond is the Michaehs-Arbusov reaction, which is a characteristic reaction of tricoordinate phosphoms compounds containing an alkoxy group (22). Alkylation of the electron pair is followed by rearrangement of the initial phosphonium salt. 

Bromo-j3-nitrostyrene and triphenylphosphine in dry benzene gave the phosphonium bromide (47). Using methanol as the solvent, the rearranged product (48) was formed, possibly via an azirine intermediate. Substituted -bromo-/3-nitrostyrenes yield the phosphoranes (49) and a phosphonium salt. When the aryl group is electron-donating, the reaction follows a different course to form the styrene (50) by initial attack of the phosphine on halogen. 

The arylation reaction can be extended to bis- and tris-(dialkylamino)phosphines73, but in the case of iV-ethylanilinophosphine the reaction takes place with a rearrangement of the phosphasemidine type483. A structural transposition also occurs in the alkylation of some N-silylaminophosphines484-487 (reaction 141). Finally, it is noteworthy that, as far as the tris(dimethylamino)phosphine is concerned, many polyhalomethyltris-(dimethylamino)phosphonium salts have been prepared by the action of the appropriate polyhalomethanes (reaction 142). 

This reaction based on the petrochemical crude material isobutylene makes the synthetic route to P-ionone (36) substantially shorter and cheaper, especially since the isomeric double bond proves to be advantageous in the subsequent reactions. In addition, i-methylheptenone (37 a) can be converted into methylheptenone (37) by noble metal-catalyzed isomerization. The reaction steps ethynylation (C2 addition), Carroll reaction (C3 addition), ethynylation and partial hydrogenation (C2 addition) lead from methylheptenone (37) via dehydrolinalool (42), pseudoionone (43) and p-ionone (36) to the C15 alcohol p-vinylionol (44). With triphenylphosphine (15), the desired C15 phosphonium salt (13), which is the second important synthetic building block for vitamin A and carotenoids16), is obtained directly from p-vinylionol, by allyl rearrangement. 

The adduct 65 of aziridine to the acetylenic phosphonium salt 64 readily rearranges to the enamine 66, which in refluxing acetonitrile is converted into the pyrroline derivative 68 by opening of the aziridine ring and recyclization of the resulting zwitterion 67 (equation 33)54. 

The dihydropyridine derivative 236, a cyclic enamine, is formed from crotonaldehyde and the phosphonium salt 235 by a Wittig reaction, followed by electrocyclization of the resulting 1,3,5-triene. The dihydropyridine readily rearranges to the tetrahydropyr-idine 237 by a [1.5] hydrogen shift (equation 99)122. 

Ammonium and phosphonium salts with relatively large nuclear hyperfine coupling constants for N and P provide only out-of-cage products, i.e., bibenzyl. While an arsonium salt, on the other hand, provides mainly in-cage radical coupling, i.e., rearrangement, due to a smaller nuclear hyperfine coupling constant... 

A combination of triphenylphosphine and diethyl azodicarboxylate (the Mitsunobu reagent) is useful for the rapid conversion of aromatic hydroxamic acids (211) to 0-(yV-arylcarbamyl)hydroxamates (212), products of the Lossen rearrangement. In some cases, a spontaneous second Lossen rearrangement occurs to give diarylureas (213), as shown in Scheme 33. The yields of (212) and (213) are 70-85%. The intermediacy of the phosphonium salts (214) has been suggested. 

Lawrence, N. J., Muhammad, E. Ramberg-Backlund type reactions of phosphonium salts. Tetrahedron Lett. 1994, 35, 5903-5906. Wladislaw, B., Marzorati, L., Russo, V. P. T., Zim, M. H., Di Vitta, C. Novel reaction decarboxylative Ramberg-Backlund rearrangement in some a-isopropylsulfonyl carboxylic esters. Tetrahedron Lett. 1995, 36, 8367-8370. 

The bis-phosphonium salt (158) promotes the Lessen rearrangement of phenyl-hydroxamic acids and also brings about the Beckmann rearrangement of ketoximes under mild conditions. The salt (159), (formed from the reaction of 2-hydroxyethyl-triphenylphosphonium chloride with phosgene) has been employed as an amino-... 

The reaction between 1,8-bis(bromomethyl)naphthalene and Ph2PSiMe2 affords a cyclic phosphonium salt (1), which can be rearranged with Me2P=CH2 to give the cyclic ylide (2). 

Alkaline hydrolysis of the spiro-phosphonium salt (83) gave the oxide (84) with no product derived from an expected Wittig-Stevens rearrangement. 

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