Stable Phosphazenium Ions in Synthesis—an Easily Accessible, Extremely Reactive “Naked” Fluoride Salt

Abstract

The electrophilic character of tin in the new compounds 3 is manifested in reactions with n~c l e o p h i l e s .~'~~ With pyridine and with 2,2'-bipyridyl, 3a forms the adducts 6a and 7a, ["] in which the tin atom is coordinatively saturated (cf. Table 1, ' 9Sn resonance signals at high field). As in the case of 3a, dynamic processes can also be demonstrated for 6a and 7a by 'Hand I3C-NMR spectroscopy. The structure for the intermediates 4 is based on consistent sets of NMR data (cf. Table 1 for 4b) and is confirmed by the isolation of the final product 5. The results suggest that the formation of compounds 4 and 5 from 3 and 4 respectively proceeds via an Sn-Substituted vinyl cation 8. [Z 4586 IE] German version : Angew. Chem. 103 (1 991) 1374 CAS Reeistrv numbers:[9] 3b, 3c, 3d, 3e: relevant 'Hand I3C NMR data correspond to the values for 3a. 119Sn/11B NMR (CD,CI,, 298 K): 6("9Sn)/6(1'B) = + 207.5/ -4.9 (3b); + 203.1/-4.5 (3c); + 2232-4.3 (3d); + 202.1/-4.4 (3e).[lo] R. Boese, D. Blaser, J Appl. Crysrallogr. 22 (1989) 394.[11] X-ray structure analysis of 3a at 115 K : P2,/c, a = 11.924 (2), b = 14.512(3), c = 14.299(2) A, a = y = 90". = 97.29(1)", V = 2454.4(7) A3, 2 = 4, e,.,,, = 1.274 gcm3, p = 1.05 mm-', Mo,. radiation (graphite monochromator), i . = 0.71069 A; 3414 independent reflections. 2979 observed (4 2 4c(F)); 2@(max) = 45"; absorption correction: empirical, Y scans in the 28 range, r): 3 2 35 max/min. Transmission: 0.926/0.815, R,,,,

Quantitative Measure for the “Nakedness” of Fluoride Ion Sources

“…Because the free energy change, zfG, is a quantitative measure for the tendency of a reaction to occur,^ the calculation of AG for process (1) AG CFCs) + A(g) -> C^AF(s) (1) provides a quantitative measure for the fluoride donor ability of C"^F" and hence the "nakedness"…”

“…The function [k AV -S°298(A,g)] on the right hand side of equation (10) and equal to the entropy change for process (1) can thus be seen to be independent of the actual choice made for the cation C, and hence the quantitative measure of the "nakedness" of the fluoride ion sources is vested in the enthalpy (rather than the free energy) change for reaction (1). Thus, while z(G(kJ mol'^) at 298 K for reaction (1) is given by equation (12),…”

Secododecahedradienes - Syntheses, Reactivity, in-Plane Homoconjugated 3C/2e Cations, 4C/3e Radical Cations, andσ-Bishomoaromatic 4C/2e Dications?

“…Since, in contrast, monoepoxidation at the stage of disecodienes is less problematic, the synthesis of 40a,b was started with the oxidations 21a 3 42a and 37 3 42b; with equivalent amounts of peroxycarbamic acid, the ene epoxides, 42a,b were selectively produced and, inductively stabilized, survived chromatographic separation. Yet, whilst 42b proved amenable to S N 2 cyclization with P 2 F as base [35] (3 85% of 40b), 42a was largely destroyed under the S R 2 conditions (Li/HgTHF). Bisepoxide 43 was isolated after exhaustive epoxidation of a product mixture obtained after an incomplete conversion 18a/30 3 2a (mainly 32), in agreement with the sequence of events formulated in Scheme 3.…”

Glycosylidene Carbenes part 26. The intramolecular F…︁HO hydrogen bond of 1,3‐diaxial 3‐fluorocyclohexanols

“…202 (27). 183 (56 [63] (19.2 g. 78.0 mmol), Iff-imidazole (13.7 g, 200 mmol), and f-BuMe,SiCI (15.7 g, 100 mmol) in D M F (60 ml) was stirred for 30 min at 23", evaporated (46'/ < 1 Torr), diluted with hexane/AcOEt 1 :3, washed (H,O, brine), and dried (Na,SO,). FC (hexane/AcOEt 1.4 -t 1 :2) gave the disilyl ether 28 (8.39 g, 21 YO).…”