J. Am. Chem. SOC. 1981, 103, 727-728
727
Hz); I3C NMR (CDC13) 171.13 (C3), 34.28 (C4), 41.68 (C5), 42.24 ( c & 5.71 (C6-CH3) ppm. The further structural confirmation of both 6b and 6c was based on comparisons of 'H and I3C NMR spectra with those of 3-phenyl-6,6'-dimethyl-1,2-diazabicyclo[3.1.0]hex-2-ene (6d) (mp 52.5 "C) obtained from the decomposition of 4d (mp 120 OC)'O in 59% yield'* [a: UV (max in EtOH) 254 nm (log e 4.14); m/e (re1 intensity) 186 (M', 4%), 158 (23%), 143 (loo%), 128 (62%), 115 (33%); 'H NMR (60 MHz in CC4) 6 2.90 (dd, endo-C4-H, J = 4.0 and 18.0 Hz), 3.10 (exo-C,-H, J = 8.0 and 18.0 Hz), 2.45 (dd, C5-H, J = 4.0 and 8.0 Hi!), 0.92 (s, end@C&H3), 1.33 (s, exo-c6-cH3); I3C NMR (CDCl3) 171.03 (C3), 35.30 (C4), 50.07 (C5), 47.07 (C6), 11.87 (endo-C6-cH3), 25.87 (f?XO-C6-CH3) ppm]. From the above experiments, it was also found that the rates of formation of 6 and disappearance of 5 were in the order b > d > c > a. This order coincides with that of relative thermal stability of aziridines 6. Among four aziridines, 6b was found to be most stable and gave a 1:4.8 mixture of 5bI9 and 6b upon heating in refluxing carbon tetrachloride for 1 h. Similarly, 6d afforded a 1:2 mixture of 5dZ0and 6d. On the other hand, the more labile aziridines 6c and 6a afforded a 1.9:1 mixture of 5c and 6c and a 2.3:l mixture of 5a and 6a, respectively. These results provide the same thermal reversibility between aziridine and allyldiazomethane as that reported previously by u s 2 The experimental results shown here, thus, provide the high stereoselective 1,l-cycloaddition reaction of (E)-1 and (Z)-1and retro- 1,I-cycloaddition reaction of endo-2 and exo-2, supporting a concerted mechanism of an intramolecular 1,l-cycloaddition of diazomethane to the C=C double bond.
decoupling. Fundamental to NMR is the general rule that, provided the relaxation pathway of a nucleus I is dominated by 'H-I dipolar couplings, the NOE is independent of the number of relaxing protons, being 1 YH/27I provided the extreme narrowing limit appliese4 R e ~ e n t l y ,we ~ derived an expression for the decoupled enhancement, &, following a PT pulse train as a function of T and A for any nucleus of spin 1 scalar coupled to n spin '/zparticles with T at its optimum value of 0.253-', (protons). For 1 = this is
Acknowledgment. We gratefully acknowledge support of this work by the grant-in-aid for Chemical Research in Development and Utilization of Nitrogen-Organic Resources sponsored by the Ministry of Education, Tokyo, Japan.
giving the optimum decoupled enhancement factor
(18) The yield was determined by. liquid chromatography - . . using- Waters DATA MODULE 730. (19) 5b: 'H NMR (CC14) 6 1.6 (CH,), 3.0 (CH,), 5.5 (CH=CH). (20) Sd: 'H NMR (CC14) 6 1.7 (CH,), 3.2 (CHI), 5.3 (CH=CH).
Enhancement of 29Sior l19Sn NMR Signals in the Compounds M(CH3),Cld, (M = Si or Sn, R = 4, 3, 2) Using Proton Polarization Transfer. Dependence of the Enhancement On the Number of Scalar Coupled Protons David M. Doddrell,* David T. Pegg, William Brooks, and M. Robin Bendall School of Science, Griffh University Nathan, Queensland, 41 11 Australia Received August 18, 1980 Recently, Freeman and Morris' and MorrisZproposed the use of the nonselective polarization-transfer (PT) pulse train (90,H)-~-( 180,H)( 180,1)-~-(90,H) X (90,I)-A-(acquire
data, decouple)
as a general technique for enhancing the'NMR signals from a nucleus I with a low gyromagnetic ratio. The sequence is particularly useful3when the relaxation mechanism of nucleus I arises from nonproton dipolar interactions, a consequence of which is negligible nuclear Overhauser enhancement (NOE) after proton (1) Morris, G. A.; Freeman, R. J. Am. Chem. SOC.1979, 101, 760-762. (2) Morris, G. A. J. Am. Chem. SOC.1980, 102, 428-429. (3) Doddrell, D. M.; Bergen, H.; Thomas, D.; Pegg, D. T.; Bendall, M. R. J. Magn. Reson. 1980, 40, 591-594.
+
1/2n
Ed = 2 ( 1 - n ) ( y ~ / y ~ )
"C@H sin (~TJMHA)
(1)
MH=-'h
+
where y = MH l/zn, MH beiig the proton spin quantum numbers n / 2 , ( n / 2 ) - 1, . . . , - 4 2 . This series expression has the simple analytic form Ed = n(yH/y]) sin (sJA) cosw1 (TJA)
(2)
The equivalence of (1) and (2) can be shown by differentiating with respect to A the identity n
cos" (rJA) = 2-" x n C ycos [(2y - n)nJA] y=o
The first maximum of (2) occurs at A = Aopt,where Aopt = (sa-' arcsin n-'p
Edopt
= (yH/y])n'/z( 1 - 1/rI)(l/z)(w')
(3)
(4)
This shows that Edo increases as n increases while btdecreases (see Table I). In Gct for large n, Edopt (yH/yI)(n/e)'/' and bt= l/(sJ&) where e is the exponential number. Thus while Edopt = y y / for ~ ~n = 1,2, it can exceed 2yH/TI for n L 11. Such behavior 1s significantly different from that of the NOE, and large enhancements are possible for a variety of interesting systems having large n. While signal enhancements exceeding yH/yrare known,6 in this paper we show experimentally that it is possible to obtain larger enhancements and that the PT sequence is likely to be useful to boost the signal to noise ratio (S/N) of NMR of heavy atoms such as Si and Sn for which there appears to be little NOE on proton decoupling. A coupled PT 'I9Snspectrum (A = 0) of (CH3)4Snis shown in Figure 1.' Note the spectacular improvement in S/N and the change in relative intensities between the PT and FT spectra. The relative intensities should change from ( F T ) 1:12:66:220:495:792:924:792:495:220:66:12:1 (some of the outer lines are too weak to be observed) to 3:30:132:330495:396:0:-396:-495:-330:-132:-3O-3(PT). When a proton decoupling field is applied, the experimentally found 4 0.095.l-I and the S / N boost by a factor of 5.3 for the '19Sn resonance compare favorably with the theoretical values of 0.093J-' and 5.76 found from 2.147 (yH/ySn)(see Table I). For (CH3)3SnCland (CH3)zSnCl, we find that the theoretical bPt timings do give the maximum enhancements, but these are about 20% less than predicted, being 3.8 (expt) and 5.0 (theory) and
-
-
(4) Kuhlmann, K. F.; Grant, D. M.; Harris, R. K. J. Chem. Phys. 1970, 52,3439-3448. (5) P e g , D. T.; Doddrell, D. M.; Brooks, W. M.; Bendall, M. R. J. Mugn. Reson., in press. (6) Chingas, G. C.; Garroway, A. N.; Moniz, W. B.; Bertrand, R. D. J . Am. Chem. SOC.1980, 102, 2526-2528. (7) '19Sn NMR spectra were determined at 33.56 MHz on a modified HX-90 NMR spectrometer fitted with a CXP-type pulse programmer, modulator, and receiver. A hardware controlled phase shifter was available on the IH (90 MHz) channel. Phase alternation of the 90,H pulse was ~sed.'*2~ (180,H)(180,I) refocusing pulses were used in the pulse sequence at the middle of the A period to obviate the problem of large phase c o r r e c t i ~ n s . ~ J ~ J ~ Values of Jii9sn-~were (CH,)$n (5096, benzene-d6), 53.7 Hz; (CHJ),SnCI (30%, CDCI,), 59.6 Hz; (CH3),SnCl2 (2096, acetone-d6), 85.0 Hz.
0002-7863/81/1503-727$01 .OO/O 0 1981 American Chemical Society
728
J. Am. Chem. SOC.1981,103, 728-730 the Maximum Decoupled Enhancement Edopt as a Function of the Number of Scalar Coupled Protonsa 2 3 4 6 8 9 12 15 18
Table I. Values of Aopt T o Give
n
1 0.50 1 .o a T is set equal t o 0.25J-'. b
*opt Edopt
0.25 0.196 0.167 0.134 1.299 1.553 1.0 1.155 In units of J-I. In units of YH/YI.
0.115 1.772
0.108 1.873
0.093 2.147
0.083 2.389
0.076 2.610
of compounds to test the generality of PT N M R to obtain metal N M R spectra. Acknowledgment. This research was supported by capital equipment grants from the Australian Research Grants Committee. We thank Dr. Kitching, University of Queensland, for a loan of the Sn compounds. We are grateful to a referee for pointing out the analytic simplification to the first equation.
.hhAhh
Figure 1. A comparison between the coupled FT N M R spectrum (lower)
Functionalized Vesicular Assembly. Enantioselective Catalysis of Ester Hydrolysis
of Sn(CH3), with the proton polarization-transfer spectrum (upper) determined with 7 = 4.66 ms, A = 0. Each spectrum is the average of 16 scans. Pulse times were twS" = 15 ps, tWH = 24 ps.
Yukito Murakami,* Akio Nakano, Akira Yoshimatsu, and Kiyoshi Fukuya
h
I b
Figure 2. (A) I T (a), P T (b), and reverse proton-decoupled FT (c) spectra of Si(CH3)4. rwsi was 13 ps. Each spectrum is the average of four scans. EdW,= 9.2(theory 10.8). (B)Reverse proton decoupled FT (a), PT (b), and FT (c) spectra of Sn(CH3)+ Each spectrum is the average of four scans. Edopt= 5.3 (theory 5.76).
Department of Organic Synthesis, Faculty of Engineering Kyushu University, Fukuoka 81 2, Japan Received August 25, 1980 Several studies on micellar catalysis' have been carried out in order to develop stereoselective reaction sites for the hydrolysis of enantiomeric esters and understand the origins of stereoselectivity in proteolytic enzymes,2 and some of those micellar systems having chiral centerslbqcexercised moderate enantioselectivity. We have reported3 that a zwitterionic double-chained amphiphile involving an amino acid residue may form stable single-compartment bilayer vesicles in aqueous media and suggested that such vesicles may provide asymmetric recognition sites for various guest molecules. In this communication, we report the stereoselective hydrolysis of simple enantiomeric esters, L- and D-N-benzyloxycarbonylphenylalaninep-nitrophenyl esters [L-/ D - ( Z ) - P ~ ~ - P N Pas ] ? catalyzed by a synthetic functionalired membrane formed with N,N-didodecyl-Na-[6-(trimethylammonio)hexanoyl] histidinamide bromide (1).5 The present substrates would be favorably incorporated into vesicles by their intermolecular hydrogen-bonding interaction6 with an amino acid moiety placed at the hydrogen belt region and by hydrophobic
3.2 (expt) and 4.2 (theory), respectively. The reductions appear to arise from the short Il9Sn T2values for these compounds. For all three compounds there is no NOE on proton decoupling. The enhancement factors8 for the 29Siresonances in (CH3)&i and (CH3)$iC1 are much closer to the theoretical value, being 9.2 (expt) (10.8, theory) and 8.5 (expt) (9.4, theory), respectively (Figure 2). The experimental value for (CH3)2SiC12is 5.0, again somewhat less than the theoretical value of 7.8. For this compound the T2is short and a loss of intensity is to be expected by using the PT sequence. The enhancement factors presented in this paper are clearly dependent on the number of attached protons; S / N gains of the orders of magnitude measured represent a time-saving factor of 10-100 in obtaining 29Siand Il9Sn NMR spectra. It is clear that the PT sequence will be particularly useful for obtaining metal N M R signals (e.g., Io3Rh, Ia3W 57Fe 199Hg29Si Il9Sn, 207Pb, etc.) in a variety of compounds provided there is a resolvable scalar coupling and the relaxation times (Ti) are not too short, that is, for ( h , ~
