Rearrangement alkynyl

The alkynyl steroid (96) inactivates aromatase, an enzyme which catalyzes the conversion of androgen to estrogen. It has been suggested (81JA3221) that the inactivation process involves the oxidation of (96) to an oxirene which rearranges to an oxocarbene which then binds to the enzyme prosthetic group, thus inactivating it. 

The relatively slower rearrangement of alkynyl and cyano substituents can be attributed to the reduced stability of the intermediate derived by cyclization of the triply bonded substituents ... 

The analogous dimerization of alkynes over Fe(C0)5 is not applicable, so clearly a different route towards alkynylated derivatives of 25 was needed. Comparison of 25 to cymantrene suggests that metallation of the hydrocarbon ligand should be the route of choice for the synthesis of novel substituted cyclobutadienes. In the literature, addition of organolithium bases (MeLi, BuLi) to the CO ligands with concomitant rearrangement had been observed [25]. But the utilization of LiTMP (lithium tetramethylpiperidide, Hafner [26]) or sec-BuLi as effectively non-nucleophilic bases led to clean deprotonation of the cyclobuta-... 

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]. 

By organoboration of bis(alkynyl)plumbanes 85, the compound 86, stabilized by a jt-bonding interaction, is prepared180. (Scheme 22a). The cation 86 is unstable and, at room temperature, decomposes rapidly to rearrange into a l,4-plumbabora-2,5-cyclohexa-diene, 87. 

Mark, V., A facile SNi rearrangement the formation of 1,2-alkadienylphos-phonates from 2-alkynyl phosphites, Tetrahedron Lett., 281, 1962. 

In line with the known similarity between the chemistry of Si and P, alkynyl phosphorus species undergo a similar rearrangement (Eq. 2.79) [58]. 

Eq. 2.79. Rearrangement reaction of zirconacycles containing an alkynyl phosphorus group. 

E,E)-a,P Y,5-Drenones.2 Aryl a,(3-alkynyl ketones rearrange in the presence of this ruthenium catalyst in refluxing toluene to conjugated (E,E)-dienones in 75-85% yield. A similar rearrangement with alkyl a,(i-alkynyl ketones proceeds less readily. 

An entirely different situation is found in alkynyl halides. Here only examples in which the rearrangement is supported by carbonyl groups [106, 164] or electron-withdrawing pentafluorophenyl groups [165] are known. As one example, the selective reaction of the alkynyl bromide next to the carbonyl group, in the presence of a second alkynyl bromide with a propargylic C-O sigma bond, is shown (88 —> 89) [164] (Scheme 1.38). 

A little-explored route to allenylsilanes utilizes tosylhydrazone derivatives of tri-methylsilyl alkynyl ketones [52]. Treatment with NaBH3CN in acidic medium leads to transient propargylic diazines, which rearrange with loss of nitrogen (Eq. 9.44). 

Keywords Alkynyl lactams, Heck reaction, Domino-Heck type reaction, rearrangement... 

Additionally, dimedone derivative 241 and propargylamine 234 could be combined to give the alkynyl vinyl amine 242. The rearrangement/cyclization cascade could be induced upon heating until reflux in chlorobenzene. The an-... 

A hitherto unknown type of rearrangement of l-(l-alkynyl)cyclopropanols (321) to cyclopent-2-en-l-ones (322) mediated by octacarbonyldicobalt" and hexacarbonyldicobalt" complexes has been described. A possible pathway for the transformation is outlined in Scheme 101. A -proton transfer accompanied by a metal-mediated Stevens rearrangement, which converts a coordinated dimethylsulfane... 

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