From Thioesters

Tin(Il) shows considerable affinity towards nitrogen, therefore is expected to activate the imino group. The diastereoselective addition of tin(II) enolates derived from thioesters 1 to x-imino-esters 2 is reported12. This reaction proceeds smoothly to afford. vi w-/j-amino acid derivatives 3 (d.r. 95 5) in good yields. Lithium, magnesium, and zinc enolates do not react while titanium enolates give the adducts in low yield with preferential formation of the anti-isomer. 

Transesterification from thioesters to esters188 or amides189,190 (lactams) are conducted by Cu1- or CuII-based Lewis acids (Scheme 45). Addition of alcohols to isocyanates is accelerated by CuCl.191... 

Bernadi and Scolastico, and later Evans in a more effective manner, indicated that the enantioselective addition reaction using silyl enol ethers can be catalyzed by Lewis acidic copper(II) cation complexes derived from bisoxazolines [38-40]. In the presence of the copper complex (S,S)-14 (10 mol %), silyl enol ethers derived from thioesters add to alkylidenemalonates or 2-alkenoyloxazo-lidone in high ees (Scheme 12). Bernadi, Scolastico, and Seebach employed a titanium complex derived from TADDOL for the addition of silyl enol ethers to nitroalkenes or 2-cyclopentenone [41-43], although these are stoichiometric reactions. 

O-Silacyclobutyl A,0-ketene acetals (derived from thioesters) reacted more slowly with aldehydes than did their ester counterparts (Table 10) <1994JA7026, 1993JOC988>. The higher reactivity of the (l-phenyl)silacyclobutyl derivatives enabled the uncatalyzed aldols to proceed at a reasonable rate, affording the corresponding products after... 

Table 10 Reaction of O-silacyclobutyl S.O-ketene acetals (derived from thioesters) with aldehydes...

Stabilization of oxyanion intermediates derived from thioesters... 

Various substrates have been successfully used in the present LASC-catalysed aldol reaction. Aromatic as well as aliphatic, a, 3-unsaturated and heterocyclic aldehydes worked well. As for silicon enolates, silyl enol ethers derived from ketones as well as ketene silyl acetals derived from thioesters and esters reacted well to give the corresponding adducts in high yields. It is noted that highly water-sensitive ketene silyl acetals reacted smoothly in water under these conditions. 

In the presence of a catalytic amount of [(f )-l,l -bi-2-naphthaIenediolato(2)-0,0 ]oxotitanium 2, silyl enol ethers derived from thioesters reacted with cyclo-pentenone to afford the corresponding Michael adducts in high yields and up to 90% ee (Eq. (12.3)) [6]. 

As indicated in Scheme 12, the labelling studies are consistent with formation of triene (36) from thioesters (34) and (35) which themselves may be built up by the assembly sequence shown. Diol (33), in which the stereochemistry at C-3 is unknown, is proposed as a common intermediate, elimination to give either an E or Z alkene leading respectively to (34) or, after further condensation, reduction and elimination, to (35). Experiments to test this sequence with the putative intermediates fed in the form of their N-acetylcysteamine (NAC) thioesters have yet to be completed, but, significantly, feeding studies in which the putative triketide (34) has been fed as the NAC thioester, as the ethyl ester or... 

Synthesis of enamino ketones from thioamides or of (3-dicarbonyl derivatives from thioesters. 

Fig. 7. Chain-length specificities of the KS and thioesterase components of the mammalian FAS. The activities were measured using model substrates and reflect the ability of the KS to translocate saturated acyl chains from the phosphopantetheine thiol of the ACP to the active-site cysteine residue of the KS and the ability of the TE domain to hydrolyze saturated acyl chains from thioester linkage to the phosphopantetheine moiety.

Mukaiyama aldol reaction. Reasonably good enantioselection is observed when the catalyzed reaction of ketene silyl acetals derived from thioesters with aldehydes is conducted in supercritical fluoroform. ... 

Several examples of the present aldol reactions of silyl enol ethers with aldehydes in water-ethanol-toluene are summarized in table 6. 3-Pyridinecarboxaldehyde as well as 2-pyiidinecarboxaldehyde, salicylaldehyde, and formaldehyde-water solution worked well. As for silyl enol ethers, not only ketone enol ethers but also silyl enolates derived from thioesters were used. In every case, the adducts were obtained in high yields in the presence of 10mol% Yb(OTf)3. 

P-Lactones can be prepared in good yield from thioester enolates. Suggest a mechanism for the reaction shown. 

Orsellinic acid (V) and altemariol (a heptaketide) are both formed directly from thioester substrates by acyl transferase and condensation reactions, without the intervention of reductive steps. Orsellinic acid may be considered the simplest phenol in the biogenetic sense, and the mechanism of its synthesis could prove an excellent model for these systems. 

The general mechanism for acyl transfer reactions from thioesters is envisaged as a nucleophilic attack at the positively polarized carbonyl carbon, accompanied by or followed by thiol elimination. 

By performing the hydrolysis of thioesters in the presence of benzylic alcohols, transprotection of thiols could be successfully carried out in water. The reactions proceeded smoothly to give benzylic thioethers from thioesters in good yields (Scheme 3.35). 

In contrast to esters, elimination of the alkyl radical from the thiol site is the major fragmentation process. Ethylene sulfide is eliminated from thioesters with longer alkyl chains. Aromatic dithiocarboxylic acid esters usually fragment in two steps to the aryl cation. 

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