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Thioaldehydes formation

The mechanism of penicillin biosynthesis from the Arnstein tripeptide, 8-(L-a-aminoadipoyl)-L-cysteinyl-D-valine (ACV), has been extensively studied and reviewed by many chemists. Most of the biosynthetic mechanisms have been ascertained by Baldwin and Bradley using an excellent enzymatic technique.55 However, the first step in the biosynthesis of penicillin, conversion of the Arnstein tripeptide to a cis-P-lactam intermediate, is still a fascinating mechanistic problem. Although Baldwin et al. recently proposed a mechanism involving an iron-bound thioaldehyde formation route via a Pummerer-type cyclization, the intermediate for this mechanism has not been identified. The mechanism of selective formation of the cw-P-lactam ring is still also unknown (Fig. 39).56 These types of biomimetic reactions have been chemically studied. An example of an unsuccessful intramolecular Pummerer cyclization of the sulfoxide involving a cysteine moiety under standard Pummerer conditions was reported by Wolfe et al.57 Although Kaneko reported the conversion of the very simple 3-phenylsulfinyl propionamide into a P-lactam with TMSOTf/triethylamine,58 a successful biomimetic synthesis of... [Pg.241]

The reaction of [Rh(C2H4)2(T75-G Me5)] with an excess of thiophene in benzene solution led to dimerization of thiophene and to formation of the unusual binuclear complex 28. The bridging ligand can be considered as an co-mercapto a,/3-unsaturated thioaldehyde.79,152 When [Co(C2H4)2... [Pg.150]

The reactions of dinuclear thioaldehyde and -ketone complexes with PR3 take a different course. When the dimeric complexes 112 are treated with PMe3 a Ti-S bond in 112 is cleaved and the monomeric complexes 113 are reversibly formed (see Scheme 26), 69 The reaction of 112 with benzene-thiol led to a Ti-C cleavage and formation of 1,3-propanedithiolato-(phenylthiolato) complex.69 The reaction of binuclear p-191 rf-thioketone molybdenum complexes related to 115 (M = Mo, E = S, R = Aryl) with P(OEt)3 also gave mononuclear complexes [Mo(CO)2(Et) i72-S = C(Aryl)2 (i75-C5H5)] by a rather complicated reaction sequence. When other phosphites were employed additionally binuclear complexes derived from addition of the phosphite to one molybdenum atom were isolated.225... [Pg.177]

Type II intermolecular ene reaction of thioaldehydes was reported by Vedejs and coworkers492 and already mentioned by Schaumann1. Type in has recently appeared and involves the formation of a C—S bond instead of a C—C bond, as in the case of type I. Type III intramolecular ene reaction has been reported for thioketones and for thioaldehydes. The group of Motoki489 examined the thermal cyclization of o-(2-substituted allyloxy) thiobenzophenones 137 leading to 1,5-oxathiocine derivatives 138 (equation 148). [Pg.1455]

Only one isolated example of formation of thioketene and thioaldehyde dimolybdenum complexes has been reported507, but in contrast, zirconocene thioacetaldehyde and thiobenzaldehyde complexes, introduced by Buchwald, have been the subject of several studies508, including their application in the synthesis of novel antimony thiametallacy-cles 148509 (equation 156). Compound 146 was generated in situ and, after reaction with alkynes, gave rise to metallacycles 147 which, by treatment with SbCR, afforded 148. [Pg.1458]

A novel synthesis of a-unsaturated sulfines has been introduced by Bra-verman et al. [99]. Et3N or DABCO treatment of allylic and benzylic tri-chloromethyl sulfoxides triggered the elimination of chloroform and formation of the sulfines. It must be stressed that these sulfines are thermally relatively stable, and this stands in high contrast to the corresponding thio-carbonyl compounds unsaturated thioaldehydes cannot be monitored under the same experimental conditions and have to be used at very low temperature or trapped in situ. The first synthesis of thioacrolein S-oxide was achieved by flash vacuum thermolysis of an anthracene allyl sulfoxide [100], and both isomers in a (Z E) ratio of 78 22 were characterised by NMR spectroscopy at -60 °C. [Pg.138]

The reaction of alkoxides with thioaldehyde S-oxides, generated from sul-finates, was carefully examined by Baudin et al. [163]. A number of products were isolated, formation of which was explained by carbophilic addition of the alkoxide anions. [Pg.148]

In the a-elimination mechanism (39) as shown in Equation 9, hydrogen extraction by the base alpha to the sulfur results in formation of a carbanion which may rearrange via route a or b c to give cysteine and a thioaldehyde which decomposes in alkaline solution to an aldehyde and hydrogen sulfide. Thus, the stoichiometry of this reaction is (Equation 10) ... [Pg.150]

These observations, along with kinetic isotope effect studies and Hammett correlation studies, support a concerted elimination by a-bond metathesis involving a four-membered transition state (Eq. 2) [23]. A large kinetic isotope effect is observed for the loss of methane from methyl amide complexes lb and lh (Eqs. 3 and 4), comparable to those observed by Buchwald and coworkers for formation of zirconium rj2-thioaldehyde complexes [25] and by Bercaw and coworkers for formation of tantalum rf- imine complexes [5a] through similar transition states. [Pg.4]

Since 1,2,5,6-tetrathiocine 3 (see Sections 14.09.2 and 14.09.9.1.2) is unstable toward irradiation and even room light, upon irradiation in a benzene solution, the thiocine 3 formed the bicyclic compound 33 in low yield together with a polymer, as the main product (Equation 8) <1996AGE2357>. Irradiation of 3 in the presence of a large excess of 2,3-dimethylbutadiene hindered the formation of the polymer, and the bicyclic product 34 was obtained together with a small amount of the symmetrical bicycle 33 (Scheme 1) <1996AGE2357>. This indicates the formation of the intermediate thioaldehyde 35 by photochemical rearrangement of thiocine 3, while several mechanisms are plausible for the formation of the symmetrical 33. [Pg.524]

Segi et al. reacted some aldehydes with bis(trimethylsilyl) sulfide in THF with n-BuLi as catalyst. The thioaldehydes (41) thus formed were trapped with cyclopentadiene to afford adducts 42 as a mixture of endo and exo isomers (88JA1976). French workers have recently reported a gas-phase synthesis of thioxoethanal (44) from precursor (43) 44 was detected as an intermediate by photoelectron spectroscopy and by the formation of adduct 45 (90JOC2596). [Pg.11]

Thioaldehydes have been used as heterodienophiles in cycloadditions (Diels-Alder or 1,3-dipolar) mainly in connection with attempts to show the formation of the transient thioaldehydes by trapping in situ. During... [Pg.11]

Couture showed that methyl- and dimethylthiophene on irradiation in a primary amine gave pyrroles and proposed a mechanism where the first step is the formation of a thioketone or a thioaldehyde by analogy with furan photochemistry (Scheme 2).7... [Pg.172]

The Norrish Type II reaction of the peptide (68) at room temperature leads to the formation of acetophenone and oligomers of the thioaldehyde (69) (shown as its enol).67 The thio-enol (69) (characteristic u.v. absorptions at 335 nm were... [Pg.223]


See other pages where Thioaldehydes formation is mentioned: [Pg.135]    [Pg.93]    [Pg.150]    [Pg.150]    [Pg.103]    [Pg.88]    [Pg.135]    [Pg.135]    [Pg.164]    [Pg.1091]    [Pg.305]    [Pg.131]    [Pg.128]    [Pg.1273]    [Pg.2256]    [Pg.2]    [Pg.15]    [Pg.21]    [Pg.539]    [Pg.135]    [Pg.1275]    [Pg.1275]    [Pg.135]    [Pg.212]    [Pg.555]    [Pg.555]    [Pg.369]    [Pg.739]    [Pg.1273]    [Pg.223]    [Pg.571]    [Pg.2255]   
See also in sourсe #XX -- [ Pg.2 , Pg.55 ]




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