Thiazolidines proposed formation mechanism

The Rh-catalyzed ring-expansion reaction of thiazolidine 246 in the presence of a catalytic amount of KI (2 mol%) at 180°C and 65 atm of CO gave thiazolidinone 251 in 56-88% yields. Formation of thiomorpholinone 252 was not observed at all. Thus, a proposed mechanism of this reaction involves the elimination of a ketene molecule from a key intermediate 248 to form rhodathiazolidine complex 249, which undergoes migratory CO insertion, followed by reductive elimination to yield thiazolidinone 251 (Scheme 36). ... 

An unexpected formation of 2,4-disubstituted-l, 3,5-triazines (3) occurs when 3-dimethoxy-methyl-2-(lV-cyanamino)thiazolidine (2) reacts with secondary amines. When the reaction is carried out in the presence of methanol or ethanol, or with a mixture of amines, a mixture of substituted products is obtained. The proposed mechanism tor the reaction is shown in Scheme 2 [94CC2301]. 

Since direct analyses for formaldehyde and methyl glyoxal are difficult with gas chromatography (GC) or any other methods, we attempted to determine levels of formaldehyde and methyl glyoxal in various food samples using their derivatives thiazolidine and 2-acetylthiazolidine, respectively. The proposed mechanism of thiazolidine formation from cysteamine and corresponding aldehydes is shown in Figure 1. 

Figure 2. Proposed mechanisms of thiazolidine and tetrahydro-1,4-thicaine formation in cysteine-sugar systems (on the analogy of Kallen (9) and Hodge...

A proposed mechanism for the formation of the Amadori compounds of cysteine is shown in Figure 2. In this scheme the Schiff s base 6 is die key intermediate to the formation of both the thiazolidine and the Amadori compound. At pH < 7, the route to Amadori compounds is preferred. This is concluded from the observation diat the most reactive sugars (those that show highest conversion to condensation products 6 and 7) show also die highest rate of browning and flavor development (Figure 3a). Apparently, the equilibrium between compounds 6 and 7 lies then frr enough to the side of Schiff s base 6 to allow its... 

Scheme 10 shows a proposed scheme of the overall reaction catalyzed by IPNS [161]. Mechanistic studies have been performed using kinetic isotope effects [166-168] and substrate analogues [153, 169-178] by Baldwin et al. Based on these reactivities, it has been proposed that an enzyme-bound P-lactam intermediate attached to the iron(IV) (ferryl) center is formed and that the complex reacts to complete carbon-sulfur bond formation by a free-radical mechanism. Each ring closure inhibits a marked primary kinetic isotope effect and monocyclic products without thiazolidine ring closure are formed by using ACV analogues. It was shown that the C-S bond formation proceeds with complete retention of stereochemistry [179] and that an epoxide is formed from... 

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