13C NMR Analysis as a Useful Tool for Structural Assignment of Vinyl- and Dienyltin Derivatives

Abstract

During the last decade, vinyl-and dienyltin derivatives have been extensively developed and used in organic synthesis. 1 H NMR analysis of these compounds was the first analytical tool employed, together with 119 Sn NMR, for the assignment of the E or Z stereochemistry of vinylstannyl derivatives. In this paper we want to show that 13 C NMR is a powerful tool for structural analysis of vinyl-and dienyltin compounds. Chemical shifts and 13 C-119-117 Sn coupling constants are reported for several examples. In all cases described, the 3 J 13 C -119-117 Sn values give the most definitive argument for structural assignment. 1 J, 2 J and 3 J 13 C-119-117 Sn coupling constants are also reported, along with the a, b, g, and d effects of the stannyl group. When the vinyltin function is functionalized with a heteroatomic substituant, some important changes occur in the chemical shifts and coupling constants. Some examples are given in the a-oxygen, -sulfur, -halogen, -silyl, and -tin substituted vinyltin series.In the course of total syntheses of natural products, new strategies have been developed for the construction of unsaturated fragments, which are based on the preparation of vinyl-, dienyl-, or trienyltin derivatives. These derivatives are later engaged in Sn/halogen exchange, Sn/Li transmetallation, or in cross-coupling palladium-catalyzed reactions. 1 The assignment of the E or Z stereochemistry of the stannyl derivatives can usually be resolved using spectroscopic methods such as NMR techniques, but information is often omitted or contained in footnotes or supplementary material of short papers, and thus is difficult to collect except in the case of 1 H or 119 Sn NMR data.It is well know that tin possesses three 1 / 2 spin isotopes, 115 Sn (0.3%), 117 Sn (7.5%) and 119 Sn (8.6%).Sn spin-spin coupling constants can be observed and measured. 2 119 Sn NMR is a powerful analytical tool, 3 giving tin atoms chemical shifts, which are typical of the nature of the tin atom substitution. However no structural proof can be deduced from these data, excepted for deuterium containing derivatives. 4In the case of alkyltin compounds, Singh by 1 H NMR measured the 1 J, 2 J, 3 J and 4 J 1 H-119,117 Sn NMR coupling constants. 5 In a 13 C NMR study, Kuivila et al. established a "Karplus-type" correlation between the value of 3 J 13 C- 119,117 Sn and the dihedral angle of the coupling nuclei.For vinyltin derivatives, the 1 J, 2 J, 3 J and 4 J 1 H-119,117 Sn coupling constants are also well known. The 3 J H-=-Sn which appears to be the most interesting argument for stereochemical assignment, by Leusink 6 clearly shows that 3 J H(Z)-=-Sn values vary from 75.0 to 50.0 Hz whereas the corresponding 3 J H(E)-=-Sn values range from 120.0 to 90.0 Hz (Figure 1). 7 In most cases, the values of 3 J H-=-Sn allows unambiguous structural determination for bprotonated vinylstannanes.However, the measurement of 3 J H-=-Sn coupling constants becomes difficult due to multiplicity of the signals and/or overlap between stannyl satellites and other s...

Stereoselective Synthesis of Difunctionalized 1,3‐Dienes Containing Tin and Sulfonyl Groups by Palladium‐Catalyzed Regio‐ and Stereocontrolled Addition Reactions

“…[26] A possible mechanism for the hydrostannylation of (E)-1-sulfonyl-substituted 1,3-enynes 3 is outlined in Scheme 2. The mechanism is based upon those proposed by Greeves, [27] Gevorgyan, [28] and Lautens.…”

Palladium-catalyzed stereoselective hydrostannation of substituted propargyl alcohols with trineophyltin hydride

“…Also, the 2 J( 13 C, 119 Sn) geminal coupling constants with values ranging from 40.0 to 23.7 Hz for adducts 2, 4, 6, 8, and 10 (see C(1) in Table 2,) confirm that the vinyl groups are terminal. Similarly, 3 J( 13 C, 119 Sn) trans coupling constant values of compounds 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21 range from 67.8 to 60.2 Hz (see C(1) in Table 3) demonstrating the (E) stereochemistry of these adducts [7].…”

“…The 13 C NMR chemical shifts (Tables 2 and 3) were assigned through the analysis of the multiplicity of the signals by means of DEPT experiments and taking into account the magnitude of n J( 13 C, 119 Sn) coupling constants. Thus, the values of 2 J( 13 C, 119 Sn) geminal coupling constants for adducts 12, 14, 16, 18, and 20 (see C(1), Table 2), within the range 31.7-22.7 Hz indicate that the configuration of these compounds is (E) [7]. The (E) configuration of these compounds is confirmed by the fact that the values of their 3 J( 13 C, 119 Sn) coupling constants lie between 61.2 and 54.8 Hz, indicating that the R substituent at C(3) is trans with respect to the the organotin moiety attached to C(2).…”

“…In the case of compounds 2, 4, 6, 8, and 10, the 1 H NMR spectra also show that attached to C(3) there is another proton (H B ) with 3 J(Sn,H) coupling constants values of around 140 Hz, indicating a trans relationship between this proton and the triorganotin group attached to C(2). Similarly, the 1 H NMR spectra of the adducts resulting from the b-syn attack, compounds 3,5,7,9,11,13,15,17,19, and 21 (Table 3), also show in all cases signals between 5.10 and 6.20 ppm corresponding to the proton attached to C(2) (H A ) with 3 J(Sn,H) coupling constants values between 66 and 77 Hz indicating that this proton is cis with respect to the organotin substituent attached to C(3). Also, in the case of the adducts resulting from the hydrostannation of the terminal propargyl alcohols, i.e., compounds 3, 5, 7, 9, and 11, the 1 H NMR spectra show signals corresponding to a proton attached to C(3) (H B ) with 2 J(Sn,H) coupling constants values between 76 and 72 Hz indicating that this proton and the organotin moiety are geminal.…”

Use of polymer-supported phenyltin for the creation of aryl–aryl or aryl–heteroaryl bonds via Stille cross-coupling reactions

“…In addition, numerous total syntheses of highly functionalized compounds have implied a Stille cross-coupling reaction in the final steps [7][8][9]. This is mainly due to the air-and moisture-stability of organotin substrates, to the compatibility of the reaction with virtually any functional group [2][3][4][5][6][7][8][9][10], to the availability [10][11][12] and to the easy characterization of organostannanes [13][14][15][16].…”