TOCSY and ROESY

These experiments are characterized by a mixing time during which the magnetization of a spin A, submitted to a radio wave frequency field Bl is transferred to a spin linked to A either by a dipolar coupling or by a scalar coupling. During the mixing time the magnetizations are locked according to one direction of the space defined by the direction of the field Bl and the spin frequency shifting versus the main component. The block in the spin system is commonly named spin-lock.

TOCSY ou HOHAHA :

This method allows to demonstrate scalar couplings. The pulse sequence scheme is given Fig. 23. The first 90°x impulsion rotates the magnetization vectors in the xOy plane, in which they freely evolve during the time tl, under the influence of their chemical shift and the scalar coupling constants. We apply then a spin lock on the x axis, that means a low power impulsion or set of impulsions whose duration represents the mixing time tm. During this time, the spin coherence of the system is exchanged. By increasing the mixing time we increase the number of the visible transitions. That is to say that within the same experiment, we get the informations of a COSY, of a LR COSY and of a relayed COSY. The pulse sequence widely used is base upon the MLEV-17 sequence which contains a set of 17 pulses.

Fig. 29 : Saccharine molecule

Fig. 23 : The pulse sequence TOCSY or HOHAHA

The spectrum 10 shows the result of three different mixing time for the saccharose (Fig.29). These are given in milliseconds (20, 60, l00 ms). For each mixing time, we see the appearance of new correlation spots. There is thus an increase of the number of relays with the spin lock time. These ones correspond then to long range correlations.

Spetrum 10: 20ms, 60 ms, 100ms.

Tocsy 20

Tocsy 60

Tocsy 100

ROESY ou CAMELSPIN :

The aim of the dipolar correlation experiments in two dimensions is to take advantage of the vicinity in space of some nuclei. The result of this kind of experiment is a 2D map in which the signals outside of the diagonal arise from the Over Hauser enhancement effect between two space coupled nuclei(Fig.24).

Fig. 24 : The ROESY pulse sequence

In this case, we apply a spin-lock onto the y axis. The correlation peaks arising from the ROE effect are on the opposite sign compared to the diagonal one their intensity is different from 0. However, the correlation peaks coming from a chemical exchange are of the same sign than the crossing one. The ROESY experiment allows by this way the separation of the contributions coming from the exchange and those coming from the dipolar interactions. The ROESY sequence is thus complementary of the NOESY one and it is more often used for the structural determination of the small molecules.

The regioselective synthesis of spirooxindolo pyrrolidines and pyrrolizidines via three-component reactions of acrylamides and aroylacrylic acids with isatins and α-amino acids

Beilstein J. Org. Chem. 2014, 10, 117–126.
http://www.beilstein-journals.org/bjoc/single/articleFullText.htm?publicId=1860-5397-10-8

The three-component condensation of equimolar amounts of isatins 1, α-amino acids 2 and acrylamides 3 in boiling aqueous methanol (1:3) afforded the spirooxindoles 4a–4g in moderate to excellent yields (Table 1). The reaction times largely depend on the reactivity of the employed α-amino acid. The longest reaction time (7 h) was found for sarcosine, while the fastest reaction (40 min) was found for proline as a substrate (Table 1, entries 1 and 3).

Table 1: Three-component synthesis of spirooxindoles 4a–4g.

entry	compound	R1	R2	R3	R4	R5	yield (%)	time
1	4a	H	Br	CH3	H	H	31	7 h
2	4b	H	NO2	CH2CH2CH2		H	85	3 h
3	4c	H	NO2	CH2CH2CH2		CH3	37	40 min
4	4d	H	Br	CH2SCH2		H	42	1 h
5	4e	H	NO2	CH2SCH2		H	60	6 h
6	4f	4-CH2C6H4Cl	H	CH2SCH2		H	38	2 h
7	4g	CH3	Br	CH2CH2CH2		CH3	58	2 h

The 1,3-dipolar cycloaddition of unsymmetrical dipolarophiles such as acrylamides can occur via the two pathways A and B leading to the formation of the regioisomers 4 and 4’. In our case, spirooxindol 4 is exclusively formed. All new cycloadducts obtained by the above method were characterized by mass spectrometry, 1H and13C NMR, and elemental analyses. The regiochemical outcome of the cycloaddition was unambiguously confirmed by NOE experiments in 1H NMR as well as later by a single crystal X-ray structure analysis of the cycloadduct 4a.

The 1H NMR spectra of compounds 4b–4d have two multiplets at 4.07–3.72 ppm for 7a’-CH and 3.50–3.35 ppm for 2’-CH (compound 4b) or 6’-CH (compound 4d) and a singlet at 1.45 ppm for 2’-CCH3 of compound 4c. The relative stereochemistry of compounds 4b–4d was established by NOE cross peaks between 7a’-CH and 2’(6’-CH) and 2’-CCH3. Also, multiplets for 7a’-CH and 2’-(6’-CH) and singlet for 2’-CCH3 show correlation signals to the neighboring methylene groups. Additionally, the absence of the NOE cross peak of 4-CH of the isatin nucleus and 2’(6’-CH) or 2’-CCH3 of the pyrrolizidine moiety was indicative for the assigned relative stereochemistry. Therefore, the relative stereochemistry could be as shown in Figure 1.

Figure 1: The NOE correlations of the signals in 1H NMR spectra of compounds 4b–4d.

The NH-proton of the oxindole moiety appeared as a singlet between 10.38–10.86 ppm. The 13C NMR spectra of compounds 4a–4g showed characteristic peaks at 71–73 ppm due to the spiro carbon nucleus.

The structure of compound 4a was determined by an X-ray diffraction study of a single crystal and supports the structure deduced from NMR spectroscopy (Figure 2).

Figure 2: Molecular structure of spirooxindole 4a according to X-ray diffraction data.

COSY and NOESY Timing Diagrams

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