(1; R1 = Ph, R2 = H)

[64042-43-9]  · C14H12LiN  · 1,1-Diphenyl-2-azaallyllithium  · (MW 201.21) (2; R1 = H, R2 = Ph)


(agents for the nucleophilic aminomethylation of ketones and alkyl halides;2 react with C=C, C=N, C=S, and N=N double bonds as well as with C&tbond;C and C&tbond;N triple bonds by [3 + 2] cycloaddition with high regioselectivity and stereospecificity;3 corresponding cycloadditions with N-benzylidenebenzylamine1)

Solubility: sol THF; slightly sol Et2O.

Preparative Methods: 1,1-diphenyl- (1) and 1,3-diphenyl-2-azaallyllithium (2)4 are prepared by deprotonation of N-(diphenylmethylene)methylamine or N-benzylidenebenzylamine, respectively, with Lithium Diisopropylamide in THF or Et2O/THF at ca. -60 °C. Solutions thus prepared contain diisopropylamine. Amine-free solutions of cis,trans-(2) are obtained by thermal conrotatory ring opening of N-lithio-cis-2,3-diphenylaziridine in THF.4 cis,trans-(2) is labile4 and isomerizes readily at 20 °C1 to give trans,trans-(2); 1-phenyl-2-azaallyllithium is prepared similarly.1 Aliphatic substituted 2-azaallyllithium reagents are prepared by stannyl-lithium exchange.5

Handling, Storage, and Precautions: solutions of (1) and trans,trans-(2) in THF are stable at -30 °C under N2 or Ar for days. No special precautions are necessary.

Indirect Nucleophilic Aminomethylation and Synthesis of 2-Azabutadienes.

Reaction of (1) with ketones yields hydroxy azomethines which are of preparative interest since they provide b-amino alcohols on hydrolytic cleavage with acids (eq 1).2 Dehydration of the hydroxy azomethines with Thionyl Chloride/Pyridine provides an entry to 2-azabutadienes.2c Nucleophilic aminomethylation of alkyl bromides is also possible (eq 2).2a,c With a chiral, optically active derivative of (2), a highly enantioselective amine synthesis has been developed (eq 3).6 In addition, from the 3-cyano analog a synthesis of a-amino acids (eq 4) has been developed,7 and the 3-vinyl analog is known.8

Stoichiometric 1,3-Anionic Cycloaddition.

(1) and (2) react with C=C, C=N, N=N, and C=S double bonds as well as with C&tbond;C and C&tbond;N triple bonds by [3 + 2] cycloadditions. In contrast to unstrained isolated C=C double bonds, one of the strained isolated C=C double bonds of norbornadiene undergoes 1,3-anionic cycloaddition with (1) or (2) to give pyrrolidines.1 Compounds with an alkenic double bond conjugated with an aromatic system3,9 or an organoelement group10 (PhS-, PhSe-, Ph2P-, Ph2As-, Ph3Ge-, Ph2(O)P-, Ph2(O)As-; not PhTe-, Ph2Sb-, Ph3Sn-, Ph3Pb-) are better 1,3-anionophiles. The cycloadditions with (1) can occur with high regioselectivity (e.g. eq 5) with aryl alkenes.4 In addition, the cycloaddition of cis,trans-(2) with trans-stilbene (eq 6) or of trans,trans-(2) with trans-stilbene (eq 7) or with cis-stilbene occurs stereospecifically with respect to the alkene and the 2-azaallyl component (cis addition in each case).4,11

Cycloaddition of the 1,3-diphenyl-2-azaallyl anion (generated by a phase transfer technique) to cyclohex-2-enone derivatives yields bicyclic pyrrolidine derivatives (eq 8).12 An intramolecular 2-azaallyl anion [3 + 2] cycloaddition has also been reported (eq 9).5

(1) and (2) react with 1,3-dienes13 to afford pyrrolidines (e.g. eq 10); seven-membered cycloadducts cannot be detected.

(2) undergoes cycloaddition to aromatic azomethines and azo compounds (e.g. eq 11).14 In contrast, (1) (which is generally more prone to form open-chain adducts than 2) gives the expected cycloadduct only with p,p-azotoluene, but with azobenzene and azomethines open-chain adducts are formed.1

(2) reacts with Phenyl Isocyanate and Phenyl Isothiocyanate according to eq 12.15 (2) also reacts with phenylallenes16 to produce methylenepyrrolidines. The use of diphenylcarbodiimide and CS2 as substrates generates cycloadducts to which a secondary reaction occurs (e.g. eq 13), whereas CO2 gives an open-chain product.

It has proved impossible to effect cycloaddition of (1) and (2) with terminal alkynes or with aliphatic nitriles having a hydrogen in the a-position to the cyano group. Internal alkynes and nitriles1,17 normally react with (1) to give a cycloaddition product (e.g. eq 14). However, with (2), the corresponding aromatic ring system is generated instead of the cycloadduct (e.g. eq 15).

Catalytic 1,3-Anionic Cycloaddition with LDA as Catalyst.

Whereas, for unknown reasons, the use of N-(diphenylmethylene)methylamine (educt of 1) in such reactions has produced satisfactory results only in two cases, the yields of the cycloadducts obtained with benzylidenebenzylamine (educt of 2) are generally good, and both trans,trans-(2) and cis,trans-(2) participate in cycloaddition.1 Eq 16 shows the LDA-catalyzed polymerization of a vinyl derivative of N-benzylidenebenzylamine.1

1. Kauffmann, T. AG(E) 1974, 13, 627.
2. (a) Kauffmann, T.; Köppelmann, E.; Berg, H. AG(E) 1970, 9, 163. (b) Hullot, P.; Cuvigny, T. BSF(2) 1973, 2985. (c) Kauffmann, T.; Berg, H.; Köppelmann, E.; Kuhlmann, D. CB 1977, 110, 2659.
3. Kauffmann, T.; Berg, H.; Köppelmann, E. AG(E) 1970, 9, 380.
4. Kauffmann, T.; Habersaat, K.; Köppelmann, E. CB 1977, 110, 638.
5. (a) Pearson, W. H.; Szura, D. P.; Hartner, W. G. TL 1988, 29, 761. (b) Pearson, W. H.; Szura, D. P.; Postich, M. J. JACS 1992, 114, 1329.
6. Solladje-Cavallo, A.; Farkhanj, D. TL 1986, 27, 1331.
7. O'Donnell, M. J.; Eckrich, T. M. TL 1978, 19, 4625.
8. Wolf, G.; Würthwein, E.-U. TL 1988, 29, 3647.
9. Kauffmann, T.; Köppelmann, E. AG(E) 1972, 11, 290.
10. (a) Popowski, E. CZ 1974, 14, 360. (b) Kauffmann, T.; Ahlers, H.; Echsler, K.-J.; Schulz, H.; Tilhard, H.-J. CB 1985, 118, 4496.
11. Kauffmann, T.; Habersaat, K.; Köppelmann, E. AG(E) 1972, 11, 291.
12. Popandova-Yambolieva, K.; Ivanova, C. SC 1986, 16, 57.
13. Kauffmann, T.; Eidenschink, R. CB 1977, 110, 645.
14. Kauffmann, T.; Berg, H.; Ludorff, E.; Woltermann, A. AG(E) 1970, 9, 960.
15. Kauffmann, T.; Eidenschink, R. CB 1977, 110, 651.
16. Vo-Quangh, L.; Vo-Quangh, Z. TL 1980, 21, 939.
17. Kauffmann, T.; Busch, A.; Habersaat, K.; Köppelmann, E. CB 1983, 116, 492.

Thomas Kauffmann

Universität Münster, Germany

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