Allenes rearrangement

Alkadiene- and alkatrienephosphonates are available from acetylene-allene rearrangement of acetylene phosphites which could easily be prepared from the reaction of carbonyl compounds and 1-alkynes. 

Petrov and coworkers [41] showed that the reaction of dibromides of alkenephos-phonic acids with acetylenic alcohols involved an acetylene-allene rearrangement. The products so formed hydrolyzed easily to the corresponding phosphinic acids. The latter on heterocyclization afforded 2,5-dihydro-l,2-oxaphosphole-2-oxide derivatives (Scheme 11). 

Boisselle, A.P. and Meinhardt, N.A., Acetylene-allene rearrangement reactions of trivalent phosphorus chlorides with a-acetylenic alcohols and glycols,. Org. Chem., 27, 1828, 1962. 

The Doering-Moore-Skattebol method including a cyclopropylidene-allene rearrangement is often used for the synthesis of allenes. However, the reaction conditions applied are often not compatible with acceptor substituents. One of the rare exceptions is the transformation 76 —> 77 (Scheme 7.11) [122]. The oximes 77 are not accessible by the classical route starting from allenyl ketone and hydroxylamine (see Section 7.3.2). 

Allenes, H2C=C=CHR (R = alkyl), are metallated regioselectively at the terminal C-atom by butyllithium in THF ai low temperatures [186], Above 0 C, the metallated allenes rearrange to lithium alkynylides ... 

The various types of acetylene-allene rearrangements [la, 38-41] have been described by Jacobs [38] to involve the following processes ... 

Treatment of 3-allyl-3-(2-propynyl)-2,4-pentanedione with methyl-hydrazine to give condensation and propargyl-allene rearrangement [118]. 

The Acetylene-Allene Rearrangement. In Section 4.2.2 we discussed the base-catalyzed acetylene-allene transformation. In a study by Kitagawa et al. a useful... 

In the course of investigations on allylic and acetylene-allene rearrangements of 3-substituted quinuclidines, it was found that by oxidation and ozonolysis of compounds with functional groups at positions allylic to the double bond, not only the double bonds but also the adjacent carbon-carbon bonds are broken. For example, in the oxidation of 3-hydroxy-3-vinylquinuclidine (119), with potassium permanganate under mild conditions, and in its ozonolysis, qui-nuclidin-3-one (2) is formed along with 3-hydroxy quinuclidine-3-carboxylic acid.161 The positions of double bonds in such systems can be firmly established by NMR spectroscopy, but not by oxidative methods.101... 

Interaction of a strong base with nitrosoureas 601 led to the formation of di-azocyclopropanes 603, which proved to be less stable and to decompose via a carbene intermediate (622) (for trapping of 603, see Refs 43,101,174, 606), rearranging to allenes (624)39 3-85,88.141,174,606.607 (Scheme 16). Allene rearrangement was also reported for a cyclopropyl-l,2-bisnitrosourea 5. By the sequence 623 -4 624 allenes could be synthesized in good yields. It was shown that optical activity was transferred from the nitrosourea precursor 601 (central chirality) to the allene product 624 (axial chirality) 5o. 6s. ss... 

De Meijere, A., Faber, D., Heinecke, U., Walsh, R., Muller, T., Apeloig, Y. On the question of cyclopropylidene intermediates in cyclopropene-to-allene rearrangements - tetrakis(trimethylsilyl)cyclopropene, 3-alkenyl-1,2,3-tris(trimethylsilyl)cyclopropenes, and related model compounds. Eur. J. Org. Chem. 2001,663-680. 

The generation and chemistry of cyclopropylidene has been extensively reviewed Of the unimolecular processes, the conversion of cyclopropylidene to allene represents a synthetically important type of reaction. However, this transformation is accompanied by competitive intra-and intermolecular processes such as C-H insertions and spiro[2.2]pentane formation from insertion to alkenes. Furthermore, vinylcyclopropylidenes undergo a concerted ring expansion to cyclopentenylidene (Skattebol rearrangement). Although cyclopropylidene to allene rearrangements can occur at temperatures below — 50 C, activation enthalpies of competing processes may be lower and therefore temperature effects can play an important role in the maximization of yields. 

In the following steps (eq 7), we observed two HCl-catalyzed processes an acetylenic-allene rearrangement (to 10) and an allenic-acetylene rearrangement (to 11). While both 10 and 11 were easily identified by their characteristic NMR signals and could be distilled as a mixture without decomposition, only the final acetylene derivative (11) could be isolated in pure form after fractional distillation. Propargyl bromide reacted similarly with the three-coordinate phosphine, but in this case all of the chemical transformations occurred very rapidly and only the final acetylene phosphoranimine (11) could be isolated. 

We also obtained interesting results in studying the reactivity of acetylenic alcohols with the two-coordinate phosphines (eq 9). Depending on the position of the OH group relative to the triple bond, different types of products are obtained. In all cases, however, the first step of the reaction is addition of the 0-H group to the P=N center to yield the three-coordinate phosphine. In the case of a-acetylenic alcohols, this addition is followed by a rapid acetylene-allene rearrangement and a... 

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