Ketenimines synthesis

Alajarin M, Vidal A, Ortin MM (2003) Intramolecular addition of benzylic radicals onto ketenimines. Synthesis of 2-alkylindoles. Org Biomol Chem 1 4282-4292... 

Ketenes and related compounds have been reviewed extensively (1 9). For the synthesis and synthetic uses of conjugated ketenes see Reference 10. Ketenes with three or more cumulated double bonds have been prepared (11,12). The best known is carbon suboxide [504-64-3] 3 2 preparative uses and has been reviewed (13—16). Thioketenes (17,18), ketenimines (19—21), and their dimers show interesting reactivity, but they have not achieved iadustrial importance to date. 

KCl, dissolution process, 39 416 Ketab, synthesis, 30 263 Ketenimine complexes with iron, 12 245 KetiminoberyIlium halides, preparation and properties of, 14 307-308 a-Keto acid, formation, 43 427-428... 

Diazo(trimethylsilyl)methyl lithium (3) was found to be the reagent of choice for the synthesis of azoles from heterocumulenes (Scheme 8.43). The reaction is typically carried out in ether at 0-20 °C. Thus, alkyl- (or aryl-)substituted keteni-mines are transformed into 1,2,3-triazoles 188 (246), while C-acceptor-substituted ketenimines yield either 4-aminopyrazoles 189 or 1,2,3-triazoles, depending on the substituents (247). Isocyanates are converted into 5-hydroxy-1,2,3-triazoles 190 (248). Reaction of 3 with isothiocyanates are strongly solvent dependent. 

Reactions of this type provide one of the major routes to the commercially important l,4-benzodiazepin-2-one system (156) via the reaction of substituted o-aminobenzoph-enones (155) with amino acid esters (68CRV747, p. 756). This synthesis allows the easy preparation of 3-substituted products by the use of readily available a-substituted amino acids, e.g. the CNS active Tranxene (156 Y = C1, Ar = Ph, R1 = CC>2H) by using aminomalonic ester. Similar reactions have been carried out using other three-atom components, e.g. 2-bromoethylamine (77MIP51800) and ketenimines (77JHC99). 

Flash thermolysis of 4-substituted isoxazol-5(4//)-ones can be used to generate alkynes, isocyanides, aminoisocyanides and ketenimines (77C258, 76HCA2615). Decomposition of the oxime (538) at an oven temperature of 450 °C produces C02, benzonitrile and fulminic acid (539 equation 5) (79AG(E)467). This method thus offers a safe alternative to the synthesis of fulminic acid from the explosive metal fulminates. 

The Paterno-Biichi reaction has been employed in the synthesis, often in high yield, of a large variety of substituted oxetanes. In addition to simple aliphatic and aromatic alkenes, cycloaddition of ketones to, for example, fumaronitrile,284 l,3-diacetylimidazolin-2-one288 [Eq. (73)], and allenes286 has been reported. Allenes yield both 1,5- and l,6-dioxaspiro[3.3]heptanes as well as the 2-alkylidene-oxetane this is illustrated for benzophenone and tetramethylallene in Eq. (74). Cycloaddition of ketones to ketenimines to form 2- and... 

Ab initio calculations indicate that in the gas phase the reaction of ketene inline and formaldehyde is concerted but asynchronous whereas in dichloromethane it is a two-step zwitterionic reaction.38 The 2 + 2-cycloadditions of keteniminium triflates with imines yields 2-azetidiniminium salts with cis stereoselectivity.39 The intramolecular 2 + 2-cycloaddition of ketenimines with imines (24) provides a novel synthesis of azeto[2,l-Z>]quinazolines (25) (Scheme 9).40... 

Annelatlon reactions. The ketenimine 1 acts chemically as a vinyl phosphonate activated by the cumulated imino group and is useful as an annelation reagent for the synthesis of heterocyclic compounds. As such it condenses with the sodium salt of salicylaldehyde (2) to afford the benzopyrane in 3 in 52% yield. Similarly, the pyrrolizine 5 is available from the sodium salt of 2-formylpyrrole in 51% yield. ... 

Reactions of triphenyl-2,2-bis(trifluoromethyI)vinylidenephosphorane, synthesized from a cyclic ylide-ketone adduct. 7 Cycloaddition reactions of triphenylphosphoranylideneketenc. 8 Synthesis of triphenylphosphoranylidene-ketenimines. 9... 

The synthesis starts from 2,4,4-trimethyl-4,5-dihydrooxazole, a compound with marked C—H acidity in the exocyclic methyl group. Triple lithiation followed by derivatiza-tion with chlorotrimethylsilane affords a triply silylated, open-chain ketenimine which is reacted with [AuCl(PPh3)] in the presence of caesium fluoride to give a dimeric, octanu-clear gold(I) cluster. The reaction proceeds beyond the stage of a triauriomethyl oxazolinyl derivative which, in fact, can only be observed as a side product. 

The synthesis of A -r-butylketenimines can be accomplished readily at -80 °C. On warming to - 40 °C the ketenimines dimerized to 2-iminoazetidines (99) it is suggested that the reaction is initiated by protonation of the ketenimine. 

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