79999-61-4

Upstream product

• 554-12-1 propanoic acid methyl ester 
• 79999-62-5 thiobenzophenone S-methylide 
• 1733-15-9 Tetramethyl ethylenetetracarboxylate 
• 79999-60-3 2,5-dihydro-2,2-diphenyl-1,3,4-thiadiazole 
• 624-48-6 dimethyl cis-but-2-ene-1,4-dioate 
• 922-67-8 propynoic acid methyl ester 

Relevant academic research and scientific papers

'Thiobenzophenone S-Methylide" (=(Diphenylmethylidenesulfonio)methanide), and C,C Multiple Bonds: Cycloadditions and Dipolarophilic Reactivities

Thiobenzophenone and diazomethane afford thiadiazoline 1 at -78 deg C. By elimination of N2 from 1 at -45 deg C (t1/2 ca. 1 h), (diphenylmethylidenesulfonio)methanide (2), which cannot be isolated but is interceptible by dipolarophiles, is set free. The nucleophilic 1,3-dipole 2 undergoes cycloadditions with electrophilic C,C multiple bonds; the structures of 16 cycloadducts were elucidated. One-step and two-step cycloaddition pathways are discussed in the light of the steric course observed for (E)/(Z)-isomeric ethylene derivatives. Competition experimetns with pairs of dipolarophiles at -45 deg C and HPLC analysis of the adducts provided relative rate constants of 26 dipolarophiles, involving 2 CC, 13 C=C, 9 C=S, and 2 N=N bonds. In accordance with Sustmann's reactivity model of concerted cycloadditions, 2 shows the highest selectivity of all known 1,3-dipoles, i. e., the largest spread of rate constants (krel = 1 for methyl propiolate and 33 x 106 for TCNE). As a consequence of low LU energies, thiones are very active dipolarophiles, and fluorene-9-thione (krel = 79 x 106) stands at the top.

1,3-Dipolar cycloadditions, 116. The formation of 1,3-dithiolanes from aromatic thioketones and diazomethane - The mechanism of the Schonberg Reaction

Reactions of diaryl thioketones with diazomethane at room temperature afford 4,4,5,5-tetraaryl-1,3-dithiolanes; the scope of this surprising 2:1 interaction has been studied for decades (Schonberg Reaction). The clue to the mechanism was our observation that the stoichiometry is 1:1 at -78 °C, and 2,5-dihydro-2,2-diaryl-1,3,4-thiadiazoles are formed as primary [2+3] cycloadducts. They lose N2 at -45 °C in first-order reactions generating diaryl thioketone S-methylides which can be intercepted by thioketones (→1,3-dithiolanes), multiple CC bonds, or acids HX. In the absence of trapping reagents, the elusive intermediates either dimerize furnishing 2,2,3,3-tetraaryl-1,4-dithianes or give rise to 2,2-diaryl-thiiranes by electrocyclization. Beyond thiobenzophenone and diazomethane, our main model reaction, the studies involve fluorene-9-thione, 4,4-dimethoxy- and 4,4- dichloro-thiobenzophenone. The ring of 2,5-dihydro-2,2-diphenyl-1,3,4- thiadiazole (8) is opened by LDA at -78 °C and derivatives of anion 12 are obtained. - In summa: The Schonberg reaction consists of two 1,3-dipolar cycloadditions, linked by a 1,3-dipolar cycloreversion.

NEW REACTIONS OF THIOBENZOPHENONE S-METHYLIDE

2,2-Diphenyl-1,3,4-thiadiazoline, prepared from thiobenzophenone and diazomethane at -78 deg C, extrudes N2 at -45 deg C and allows to study in situ 1,3-cycloadditions of thiobenzophenone S-methylide (3) with electrophilic C=S, C=C, CC, and N=N bonds.