Cycloaddition reactions of 2,2,2-trifluorodiazoethane

High‐Yield Syntheses of Sodium, Potassium, and Thallium Hydrotris[3,5‐bis(trifluoromethyl)pyrazolyl]borates and the X‐ray crystal structure of {hydrotris[3,5‐bis(trifluoromethyl)pyrazolyl]borato} thallium(I)

“…This compound was obtained 1 ) by reacting 1,1,1,5,5,5-hexafluoropentane-2,4-dione with hydrazine hydrate under various conditions [13-151 and 2) by dipolar cycloaddition of 2-diazo-I, 1,l-trifluoroethane with 3,3,3-trifluoropropyne [16]. The former reaction was reinvestigated by Threadgill et al [I71 and an improved procedure of the synthesis of 1 is described here.…”

1,1,1,4,4,4‐Hexafluorobut‐2‐yne (HFB) as a Versatile Dipolarophile for [3+2] Cycloaddition with 1,3‐Dipoles toward Azoles with Adjacent CF3 Groups

“…NMR analysis of resulting mixture showed the presence of pyrazoles 4 and 5 as the main products. In this case 1,3-dipolar cycloaddition followed by sigmatropic rearrangement ( [1,5] hydrogen shift) of the initially formed 3H-pyrazole 3 gave the thermodynamically more stable NH-pyrazole 4 in 35% yield. Unfortunately, it is difficult to control the synthesis of diazo compounds quantitatively, so the main side product 5 was formed by vinylation of key pyrazole 4 with the HFB excess in 10% yield.…”

“…Pyrazoles 7 a-d (Table 1) were formed almost quantitatively by an initial cycloaddition via intermediates A and subsequent [1,5] sigmatropic rearrangements ([1,5]-hydrogen shift for entry 1 and the Alphen-Hüttel rearrangement type [1,5]-acetyl migration for entry 2 [16] ). Heterocycle 7 b under the storage Scheme 1.…”

“…The reactions were carried out in an ampoule with an equimolar mixture of reagents in DME at room temperature overnight, [b] Yields are given to the isolated products, [c] The reaction was carried out in ether, [d] The reaction was carried out at 80°C for 48 h. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 without precautions lost the acetyl group as a result of hydrolysis and was transformed to an previously described 1Hpyrazole. [9] With cyclic diazoketones 6 c and 6 d (entries 3,4) pyrazolefused heterocycles were obtained via a ring expansion owing to a sigmatropic [1,5]-acyl rearrangement. [17] However, isomeric diazotetralone 6 e failed to give the target product that may be rationalized in terms of the possible reaction mechanism of indanone ring expansion discussed previously.…”

“…In 1968 Atherton and Fields synthesized tris(trifluoromethyl)pyrazole from 2,2,2‐trifluorodiazoethane and HFB ; this synthesis was repeated with the modified procedure in 2014 . Recently the same pyrazole has been obtained via cycloaddition of HFB to easily available ethyl 2‐diazo‐3,3,3‐trifluoropropanoate .…”