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CASERIO AND KIM
TABLE 3 IR absorbances of tetramethylpiperazinium salts (KBr
pellet)
3010, 2970, 2236 (C‐D stretching),
1484, 1411, 1305
1038(BF4), 958, 954, 942, 885, 858, 840,
772 cm−1
3011, 2970, 2238 (C‐D stretching),
1618, 1478, 1326,
1300, 1038(BF4), 987, 942, 863, 807,
771 cm−1
Dimer salt
9‐d4‐2BF4
3011, 2969, 2237 (C‐D stretching),
1483, 1410, 1326,
1305, 1032 (BF4), 985, 9,54, 942, 884,
863, 840,807, 771 cm−1
3011, 2967, 1618, 1483, 1467, 1439,
1410, 1390,
1318, 1231, 1200, 1132, 1136, 1061, 1022,
972, 921, 872, 718, 634 cm−1
3010, 2970, 2236 (C‐D stretching),
1483, 1411, 1364, 1304, 1207, 1175,
1159, 1042, 1006, 984, 955, 924, 885,
858, 840, 814, 746 cm−1
3011, 2970, 2237(C‐D), 1478, 1410,
1326, 1221,
1197, 1049, 1011, 987, 944, 863, 807 cm
−1
Dimer salt cl
9‐d4‐2Cl
3011, 2969, 2236(C‐D), 1481, 1407,
1364, 1326,
(1303, 1256, 1221, 1197, 1175, 1158,
1042, 1006, 986, 954, 943, 885, 863,
839, 807 cm−1
FIGURE 1 (A) TOP: IR absorbances 800 to 900 cm−1 of A (9a‐d4‐
2Cl) 885, 858, 840; B (9b‐d4‐2Cl) 877, 863, 807; (B) BOTTOM: IR
absorbances 800 to 900 cm−1 of product mixture (as dichloride
double salts from heating 3‐d2‐BF4 (885, 864, 840, 806); 5‐d2 (885,
863, 840. 807); and a 50:50 mixture of authentic 9a and 9b‐d4‐2Cl
(885, 863, 840, 807)
Bold numbers indicate the differences in absorbances as a result of deuterium
labeling. Dimer salt data represent absorbances of product derived from the
labeled precursors, 3‐d2‐BF34 fluoroborate salt or 5‐d2.
Evidence from the deuterium labeling experiments
support the intermediacy of dimethylaziridinium ion 4
in the formation of 9.
The displacement step to form the aziridium interme-
diate 4 is a 3‐exo‐tet cyclization of the homoanomeric sys-
tem n(N) → sigma*(C ‐ X) known to be important for
favorable cyclization kinetics.[9]
with the intervention of the symmetrical intermediate
aziridium ion 4. However, NMR analysis of recovered
starting material 5 revealed that label rearrangement
had also occurred, which suggests that, in this case, the
aziridium intermediate 4 is formed reversibly from 5.
There is, however, a basic difference in the behavior of
4 depending on the nature of X. Apparently 4 is formed
reversibly from 5 (X = Cl) but irreversibly from 3
(X = Me2S). A likely explanation is that under aprotic
solvent conditions, the aziridium intermediate from 5 is
actually a tight ion pair that can readily return internally
7 | CONCLUSION
Heating (2‐substituted)‐ethylamines of the type
Me2NCH2CH2X where the X substituent is a good leaving
group (Cl− in 5, and SMe2 in 3) lead rapidly to elimination
of X and formation of tetramethylpiperizinium salt 9.