Geminal Vinyl Diazides: Potential Precursors of Functionalized Alkylidenecarbenes; Synthesis and Reactions of 3,3‐Diazido‐2‐cyanoacrylic Acid Methyl Ester

Abstract

catalyzed dehydration. 10 isomerizes to the allene 11 uia a Cope rearrangement (400-500 C). As expected[''] 11 reacts to give the diradical 12, which stabilizes itself by a 1,2-hydrogen shift to yield 4 and its nonconjugated isomer 13. Whereas at 440°C, 44% 4 and 52% 13 are produced (rest 10 and 11, GC), 13 is practically the only rearrangement product at 500°C (93%, rest 4).The structural assignments for 4 are based on 'H-and I3C-NMR data, as well as on vibrational-and electronicspectra [acetonitrile, A, , , = 252 nm (log&=3.7)]. In comparison to the conformationally less restricted 1 = 224 nm (logs = 4.411, 4 exhibits a bathochromic shift which almost corresponds to that of the completely fixed 3-methylene-1,4-cyclohexadiene [A,;,% = 242, sh at 247 nm (log&=4.41'21)].Pyrolyses of methyl derivatives of 10 result in the corresponding derivatives of 4 and 13. Moreover, since a further cross-conjugated triene (1,2-dihydropentalene) can be synthesized by thermal rearrangement of 1,2-diethynylcyclobutane, the thermal rearrangement of alkynes promises to become a useful method of preparing branched polyolefins.

Synthesis and Chemistry of Organic Geminal Di- and Triazides

“…The number of reports describing geminal vinyl diazides is, as one might expect, very small. In fact, only three molecules of this class (compounds 73 – 75 ) were synthesized until today (Scheme 15) [95,96,97,98]. It should be noted that the isolation of cyanocarbonimidoyl diazide ( 77 ) was also reported by Darzens in 1912 from the reaction of bromine cyanide ( 76 ) with sodium azide; however, the structure turned out to be wrong and was corrected by Hart in 1928 [99,100,101].…”

“…At 70 °C and 50 °C, respectively, 73 and 74 explode spontaneously. Analytical confirmation of the structures was obtained from their infrared and NMR spectra as well as from mass spectrometry in the case of methyl 3,3-diazido-2-cyanoacrylate ( 73 ) [95,96,98,102]. 2-(Diazidomethylene)malononitrile ( 75 ) is described as an orange liquid.…”

“…The first one is the unimolecular thermal or photochemical decomposition. As shown in Scheme 16, irradiation of a methanolic solution of methyl 3,3-diazido-2-cyanoacrylate ( 73 ) gives a a low yield of methyl 2-cyano-3-methoxyacrylate ( 78 ) as a by-product (besides the thermal product 88 described below) [95,96,103]. Possible intermediates for this transformation are the free carbene 79 , the diazirine 80 , the diazoacrylate 81 or the tetrazole 82 .…”

“…While the photochemical decomposition was not examined in further detail, the thermal reaction of geminal vinyl diazides is well-studied (Scheme 17) [95,96,97,98,103,104,105,106,107,108]. The key intermediate is the very electrophilic [109] double acceptor-substituted N -cyanoimine 86 .…”

“…The N -cyanoimine 86 has been characterized in solution [97,108]; all isolation attempts led to polymerization [108,109]. The existence of this intermediate 86 was also proven by cycloaddition with 2,3-dimethylbuta-1,3-diene leading to the Diels-Alder product 87 [95,96,97,108,109]. In the presence of alcohols [95,96,108,109] or amines [104,105,106,107,108], the N -cyanoimine 86 is immediately attacked at the electrophilic carbon and, after elimination of hydrogen cyanide, isolable structures 88 and 89 are obtained in good yields.…”