Pyrroline ring-opening

Five- (70, = 1) and six-membered (70, n = 2) enamines substituted in position 2 generally exist in the cyclic form. Lukes and co-workers observed that partial ring-opening occurs with the pyrroline 157) or piperideine 163,164) derivatives by atmospheric moisture. This leads to the formation... 

Reaction of 2-alkyl- -pyrrolines and 2-alkyl- -piperideines with acid chlorides leads to ring-opening and formation of N-acylated amino ketones (131, = 1, 2) (211-213). Ketene reacts with J -piperideine to form a tricyclic derivative (132) (214). 

Weak nucleophiles attack the 2-position with ring opening to form pyrrole derivatives after cyclization. The bromopseudooxazalone 62a yields the pyrroline 65 in methanolic potassium carbonate. 

The 1,3-dipolar intermediate obtained in the ring opening reaction of 3H-azirines via cleavage of the C—C bond has been trapped to give oxa-zolines 355) (3.36) and pyrrolines (3.37) 356). 

Vedejs developed an enantiocontrolled synthesis of aziridinomitosenes involving internal alkylation of the oxazole 132 to produce an oxazolium salt 133 followed by nucleophilic addition of cyanide providing the adduct 134 <00JA5401>. Electrocyclic ring opening of 134 to the azomethine ylide 135 with internal [2+3] trapping produces the tetracyclic product 137 via the pyrroline 136. 

Cleavage of aziridines has been employed in the asymmetric total synthesis of pancratistatin 57 [47], a compound that is the object of considerable attention thanks to its broad spectrum of antineoplastic activities [48]. The chemistry of vinylaziridines has for the most part been confined to their use in rearrangement sequences resulting in functionalized pyrrolines. Hence, because of the lack of data concerning the ring-opening of vinylaziridines with carbon nucleophiles,... 

The photolytic ring opening of 2//-azirines yields nitrile ylides which can be trapped as pyrrolines (97) (73JA1945). 

In neutral aqueous solution, l-(3-aminopropyl)pyrroline exists predominantly as the bicyclic tautomer, whereas in acidic solution (pD < 4.5), the Y-protonation leads to ring opening [84ACS(B)526]. 

Liberation of the organic ligand in 3-pyrroline complexes can be accomplished in good yield either by oxidation (CeIV or DDQ), or by heating under anaerobic conditions.12,14 Synthesis of the pyrrolizinone 109 is accomplished by first reducing the ring-opened 2//-pyrrolium... 

Dioxo-J2-pyrrolines (33) have been obtained from isoxazolium salts (32) by the action of alkali cyanides followed by ring-opening and reclosure.193... 

In contrast, acid chlorides normally add to Schiff bases.237,238 Ring-opening occurs on treatment of 2-alkyl-A pyrrolines and 2-alkyl- 1-piperideines with acid chlorides.239-241... 

Treatment of 2,4,4-trimethyl-/l x-pyrroline V-oxide with benzoyl chloride is accompanied by ring-opening 332 (Scheme 16). 

Under aqueous conditions dimethylamine, piperidine, and triethylamine catalyze the ring-opening reaction of 3a,5,6a-triaryl-3,3a-dihydro-2//-furo[3,2-6]pyrrole-2,6(6a//)-diones (178) <84S663> giving benzoylhydroxy-l-pyrrolines (179), which afford benzoylpyrroles (180) upon acid-catalyzed dehydration (92BCJ2611). 

In the fragmentations of cyclic diazocompounds the important considerations of sense of ring opening, disrotatory or conrotatory arise. The treatment of 3-pyrroline with nitrohydroxylamine produces butadiene and nitrogen... 

Lemal and McGregor showed that such ring openings are stereospecific and may be rationalized by the use of molecular correlation diagrams e.g. trans-2,5-dimethyl-3-pyrroline is deaminated by this procedure to pure cis, trans-2,A-hsm-diene and cw-2,5-dimethyl-3-pyrroline to the pure irons, irons isomer, viz. 

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