Pyrrolidine complexes

The best result is obtained with the (.S )-2-(2,6-dimethyl benzyl (pyrrolidine complex (see Appendix) at — 109 °C. On quenching with acid, this yields 79% of a 78 22 kinelically controlled... 

Other aminations of more substituted arene complexes allow the regiospedfic synthesis of polysubstituted aromatics. For example, p-fluoroanisoletricarbonylchromium complex can first be lithiated and quenched with chloroformate to give 33b (R = OMe, R = CChMe). After substitution of the fluoride by pyrrolidine, complex 31 is obtained in 89 % yield (Scheme 18) [29]. 

Both of the racemic crystals of the piperidine and pyrrolidine complexes have chiral space groups before irradiation. The most important requirement for the racemic-to-chiral transformation is that the two molecules with R and S configurations crystallize in a chiral space group. Since the racemic compounds tend to make a pair around an inversion center in the process of crystallization, the racemic crystals, in general, have a center of symmetry. Otherwise, conglomerate crystals may be deposited from a racemic solution. Therefore, only several crystals with chiral space groups have been reported so far [38]. This may be a reason that such a racemic-to-chiral transformation has not been observed till now. 

The anions generated from alkylamino carbene complexes can be alkylated in high yields with simple alkyl halides without any detectable amount of dialkylation. This is illustrated for the methyl pyiro-lidine complex (109), which can be alkylated cleanly with ethyl bromide to give the monoalkylated product (110) in 87% yield. The methyl pyrrolidine complex (109) can be prepared in nearly quantitative yield quite simply by treating an ether solution of the methyl methoxy complex (88a) with pyrrolidine at room temperature for a few minutes. A few examples of diastereoselective alkylations are known. The 0-alkylimidate carbene complex (112) can be alkylated with methyl triflate to give a 93 7 mixture of (113) and (114), which are diastereomers as a result of the chiral axis about the aza-allenyl linkage. Other examples of diastereoselective alkylations will be presented in Section 9.2.2.7. 

Iron-alkene complexes have also been used for the synthesis of -lactams (Scheme 25). The alkene complex (19) is transfonned into the pyrroline complex (20) on exposure to ammonia. Reduction with NaBH4 gives a mixture of stereoisomeric pyrrolidine complexes which are then converted on heating to the diastereomeric chelate (21). Oxidation with air or silver oxide produces the lactam (22). 

The Asymmetric Heck Reaction Recent Developments and Applications of New Palladium Diphenylphosphino-pyrrolidine Complexes. 

When the racemic crystal of pyrr-1 was exposed to the xenon lamp for 40 h, the cell dimensions were gradually changed with retention of the single crystal form and theratios became from 0 25 to 8 17 and 14 11 for the 1-ce groups of C and D, respectively. This means that the crystal, as a whole, changed from racanic to chiral (R S=12 28). The R S ratios of pyrr-2, pyrr-3, and pyrr-4 after photoirradiation became 72 28, 72 28, and 71 29, respectively. The pyrrolidine complex crystals also converged to about 70 30 after infinite irradiation. 

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