Thioformylation

With 2-methyl- and 2,4-dimethylthiazole, the methyl thiirenium ion (m/e 72) is obtained, which can easily lose a hydrogen radical to give the ml ell ion (confirmed by the metastable peak). This latter can rearrange by ring expansion to give the thietenyl cation whose structure was confirmed in certain spectra by the presence of a metastable peak corresponding to the decomposition of the m/e 71 ion to give the thioformyl cation m/e 45, probably by elimination of acetylene. 

Since Woodward s work on the synthesis of chlorophyll a (60JA3800) it is known that the intrinsic unstable thioformyl moiety can be stabilized by the delocalization effect of heterocyclic systems. Recently the synthesis of 2-amino- and 3-aminothioformylthiophenes (and furans) and the corresponding benzo derivatives (Scheme 19) has been reported (96S1185). These compounds exist as amino tautomers (91S609 96S1185). 

The mechanism of the condensation in Part D probably involves thioformylation of the metallated isocyanoacetate followed by intramolecular 1,1-addition of the tautomeric enethiol to the isonitrile. This thi2izole synthesis is analogous to the formation of oxazoles from acylation of metallated isonitriles with acid chlorides or anhydrides. " Interestingly, ethyl formate does not react with isocyanoacetate under the conditions of this procedure. Ethyl and methyl isocyanoacetate have been prepared in a similar manner by dehydration of the corresponding N-formylglycine esters with phosgene and trichloromethyl chloroformate, respectively. The phosphoryl chloride method described here was provided to the submitters by Professor U. Schollkopf and is based on the procedure of Bohme and Fuchs. The preparation of O-ethyl thioformate in Part C was developed from a report by Ohno, Koi/.uma, and Tsuchihaski. " ... 

This reaction exemplified that the regiochemistry of RS and H introduced by car-bonylahve addition differed from that of those by simple hydrothiolation. In the Rh-catalyzed hydrothiolation, the ArS group added to the terminal carbon and H to the internal carbon (Eq. 7.12). On the other hand, in the Rh-catalyzed thioformylation, RS was placed at internal carbon and formyl at the terminal carbon in spite of using the same catalyst precursor, [RhCljPPhsjs], which was also active for the thioformylation shown in Eq. (7.17). In 1997, the Pt-catalyzed hydrothiocarboxylation using RSH, alkyne and CO was reported to furnish 24 (Eq. 7.18), which showed the same regiochemistry as the Ni-catalyzed reaction shown in Eq. (7.1) [28]. 

The reductive behavior of iron-carbene porphyrins has been investigated. A 2g + FI" " reduction of thiocarbonyl complexes can lead to the corresponding thioformyl complexes in a reversible system [421]. 

A quantum-chemical study has been undertaken on the isomerization of ctx-1-vinyl-, -1-formyl-, -1-thioformyl-, and -l-iminomethyl-2-vinylcyclopropane to cyclohepta-1,4-diene, 2,5-dihydrooxepine, 2,5-dihydrothiepine, and 2,5-dihydroaze-pine, respectively. Reaction pathways for circumambulatory rearrangements of main group migrants (NO, PO, NCS, SCN, NCO, OCN, SR, Cl, Br, and XX where X... 

The reaction of 1-alkynes 275 gives thioformylation products 277 (Equation (21)), " while that of propargyl alcohols 278 afforded thiofuranones 280 (Equation (22)). The reaction of allenes 281 gives alkenylthiolate 282 (Equation (23)), while dithiocarbonylation took place to yield 284 in the reaction of propargylic mesylates 283 (Equation (24)). ... 

Restricted rotation in N-acetylated derivatives (377 378 AC = 61.5 kJ mol-1)362 and thioformyl derivatives 425395 has been observed by NMR, and results have been correlated with an azulene-type model (see Section VII). 

Possible routes (i) hydrolysis of thioformyl or similar derivative (ii) dealkylation of M=CHOR carbenes Scheme 1. Some synthetic approaches to transition metal formyl complexes. 

The above bond energy analysis is a relative one and does not address whether or not Eq. (2) can (despite the contrary examples above) be exothermic. Closely related hydride migrations have been observed to proceed. For instance, the thioformyl utilized by Roper in Eq. (8) was prepared as shown in Eq. (35) (52, 53). As indicated, hydride migration to coordinated CS occurs readily and in preference to coordinated CO. Since 77-bonds between first- and second-row atoms (i.e., CS) are not as strong as those between first-row atoms (i.e., CO) hydride migration (which entails a 77-bond order reduction) appears to follow the thermodynamically preferred course. 

As described in the preceding reviews on this field, most of the early work on silicon-sulfur doubly-bonded compounds was restricted to simple dialkylsilanethiones, which are all transient in solution or in the gas phase4. However, in contrast to the successful matrix isolation and spectroscopic identification of dimethylsilanone 1023, no spectroscopic detection of transient dialkylsilanethiones in matrices has been reported up to now, although the matrix isolation of Cl2Si=S50 and Cl(H)Si=S51, the silicon analogues of thiophosgene and thioformyl chloride, has been reported. 

SiS2 (125)72, Cl(H)Si=S (126)51 and Cl2Si=S (127)50 were prepared and isolated in low temperature matrices. The properties of these species are of interest as the silicon analogues of carbon disulfide (CS2), thioformyl chloride [S=C(H)C1] and thiophosgene (S=CCl2), which are well-known thiocarbonyl compounds. 

Only a few examples of this useful thermal reaction have been described. The elusive thioformyl cyanide 39 has been generated by elimination of propene from 38 upon FVP at... 

Csaszar41 for thioformyl cyanide, when comparing MP2/6-31G(d,p) and MP2/6-31 lG(d,p) optimized structures (see Table 3). 

Thioformyl and thiocarbonyl cyanides. The long-sought for IR spectrum of this compound was obtained by Wentrup and coworkers162. S=CH—CN was prepared by Flash Vacuum Pyrolysis (FVP) of allyl cyanomethyl sulfide and condensed in an argon matrix. The absorption frequencies(in cm-1) and the intensities (in km mol-1) corresponding to the five bands observed were V2, CN stretch (2221, 17) vj, CH rock (1320, 11) U4, CS stretch (1103, 10) 05, CC stretch (889, 8) vg, CH wag (824, 26). These assignments were made on the basis of MP2/6-31G(d) calculations. The spectrum of formyl cyanide is reported and discussed elsewhere163. 

The same strategy has also been applied to the preparation of a-oxothiones379 and thioformyl cyanide89 (equation 89), which were characterized by PE and IR spectroscopy. 

Thioformyl cyanide was generated under FVT conditions by retro-ene cleavage of allyl cyanomethyl sulfide as shown in equation 99. Spectroscopic properties of this compound are discussed in Section II. Note that thioformyl cyanide had already been prepared by retro-Diels-Alder reaction (see Section III F 4)... 

Mass spectral data have been obtained for compounds (20), (21), (22), and (23). The data show that the most abundant peak for each is the molecular ion. Considerable amounts of (M — 1)+ and M+2 ions are also formed. Loss of HCN from the molecular ion is evidence for the pyridine ring, while loss of carbon monosulfide and/or the thioformyl radical are characteristic of the thiophene ring <75JHC865>. Mass spectral fragmentation patterns have also been reported for the halo- and halonitrothienopyridines (Scheme 3) <70AK(32)249,74JHC205). 

A series of MO calculations has been performed on the structure, formation and nucleophilic reactivity of 1,2,3,4-thiatriazoles (1) (76AHC(20)145). However, these calculations have been criticized (see Section 4.28.2.2.3 for a detailed discussion). MO calculations have been carried out for the hypothetical ring closure of thioformyl azide 5-oxide (8 H substituted for Ph) to thiatriazole 5-oxide. It is suggested that the variable chemical behavior of thioacyl azides and their 5-oxides is due to disruption of the aromatic character of the thiatriazole 5-oxide (77T2231). 

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