Synthesis of 3-pyrrolines

Catalysts. Silver and silver compounds are widely used in research and industry as catalysts for oxidation, reduction, and polymerization reactions. Silver nitrate has been reported as a catalyst for the preparation of propylene oxide (qv) from propylene (qv) (58), and silver acetate has been reported as being a suitable catalyst for the production of ethylene oxide (qv) from ethylene (qv) (59). The solubiUty of silver perchlorate in organic solvents makes it a possible catalyst for polymerization reactions, such as the production of butyl acrylate polymers in dimethylformamide (60) or the polymerization of methacrylamide (61). Similarly, the solubiUty of silver tetrafiuoroborate in organic solvents has enhanced its use in the synthesis of 3-pyrrolines by the cyclization of aHenic amines (62). 

A fundamentally different approach to the synthesis of 3-pyrrolines is evidenced in the annulation in Eq. 13.50 [58]. Ethyl 2,3-butadienoate 150 reacts with N-sulfony-limine 151 in the presence of triphenylphosphine under very mild conditions to give JV-protected 3-pyrroline 152 in 90% yield. The mechanism that has been postulated is related to that of the Baylis-Hillman reaction. Michael addition of triphenylphosphine to the allenyl ester generates a zwitterion that combines with the imine to give 153 in a non-concerted process. This is followed by ring closure, proton exchange and expulsion of triphenylphosphine to give 152. This annulation is successful only for aromatic or cinnamyl imines [59]. 

In addition to the high regiochemistry observed, the bulky osmium pentaammine metal center also effectively blocks one face of the pyrrole ring from attack. This directs each transformation carried out on the complex to occur on the same face of the pyrrole ring. For example, in the synthesis of 3-pyrroline complex 74, both protonation and hydride addition occur from the same face of the pyrrole ring, producing 74 exclusively as the c/s-isomer. This feature is also illustrated in the synthesis of pyrrolizinone 109 vide infra), where a stereoselective hydride reduction allows the preparation of 109 as only one diastereomer. 

A rhodium-catalyzed transannulation of tosyl-triazoles 9 with silyl or alkyl enol ethers 10 was developed that allows for the synthesis of substituted pyrroles 11 with regiocontrol.The addition ofTsOH promotes the final dehydration step to afford pyrroles with different functionality. The method can also be adjusted to allow for the synthesis of 3-pyrrolin-2-ones by using silyl ketene acetals as one of the coupling partners (14TL6455). 

A gold(I)-catalysed cycloisomerization of 1,6-diynes containing propargylic esters and arenynes is reported for the synthesis of 3-pyrrolines or pyrroles (Scheme 111). ... 

Krause [222] showed that gold-catalyzed cycloisomerization of a-aminoallenes results in the synthesis of 3-pyrrolines via outer-sphere amine addition (Scheme 15.42). This early result pointed toward the application of gold-catalyzed... 

There are few reports in the literature for the synthesis of 3-pyrrolin-2-ones so a simple method for the preparation of substituted 4-phenyl derivatives from phenylpropiolic ester, dimethyl sulphoxonium methylide and amines is welcome (Scheme 64). T-Azaspiroannelation has been described by Bryson and Wilson, ... 

Synthesis of 3-pyrrolin-2-Ones from other Heterocycles... 

Early (pre-1940) interest in the synthesis of 3-pyrrolin-2-ones mainly derived from their presence as terminal groups in oligopyrrole bile pigments. 

SYNTHESIS OF 3-PYRROLIN-2-ONES FROM OTHER HETEROCYCLES... 

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