Rearrangement, predicting pathways

Predict three major fragmentation/rearrangement pathways for the above compounds. For each pathway, cite the rule from Section 1.5.4 that supports your prediction. 

Cyclization of 2-propenoic acid 2-(4-phenyl-2-thiazolyl)hydrazide (121), prepared from 2-hydra-zino-4-phenylthiazole and acryloyl chloride, with potassium carbonate yielded two kinds of thi-azolotriazepinones (122) (15% yield) and (123) (27% yield). The former, thiazolo[2,3-c]-1,2,4-triazepine (122), was the predicted product, but the production of the unexpected [3,2-6]-isomer (123) may have proceeded via the rearrangement pathway shown in Scheme 21 <82JHC747>. 

A structural perspective gave rise to predictions about reasonable rearrangement pathways for polyhedral molecules. He also measured isomerizations that confirmed the predictions. The calculations that describe the boron hydride structures also gave basis for predicting which atoms would be most reactive. These predictions stimulated much synthetic chemistry. 

The stereochemical outcome of the reaction is determined by the geometry of the transition state for the Claisen rearrangement a chairlike conformation is preferred,and it proceeds strictly by an intramolecular pathway. It is therefore possible to predict the stereochemical course of the reaction, and thus the configuration of the stereogenic centers to be generated. This potential can be used for the planning of stereoselective syntheses e.g the synthesis of natural products. 

If the reaction is carried out with ketone labeled in the C=0 group with the first pathway predicts that the product will contain all the " C in the C=0 carbon, while in the second pathway the label will be in the a carbon (demonstrating migration of oxygen). The results of such experiments have shown that in some cases only the C=0 carbon was labeled, in other cases only the a carbon, while in still others both carbons bore the label, indicating that in these cases both pathways were in operation. With a-hydroxy aldehydes and ketones, the process may stop after only one migration (this is called the a-ketol rearrangement). 

However, these are highly endothermic processes and may therefore be disregarded. (These reactions are also restricted by orbital symmetry considerations.) Thus, combining electronic and thermochemical evaluations, the preferred reaction of 48 should lead to 8. The picture that emerges from this analysis is that 47 will rearrange to 8 with 48 as a possible reaction intermediate. Overall, the reaction pathway 7 - 47 - 8 is predicted. 

Nevertheless, the agreement that is obtained - which is probably the best one should expect given the small size of the basis set used in the CCSD(T) calculations and the possible problems associated with biradical character in the methyl vinyl ether pathway - suggests that the theoretically predicted TS structures are accurate representations of the actual transition states. This establishes the concerted nature of three of the rearrangements and the stepwise nature of the fourth. 

The details of protonation of several alkyl-substituted phenanthrenes by superacids have been reported.73 The observed mono- and di-cations are usually in agreement with those predicted by AMI MO calculations. Molecular modelling studies have suggested a multi-step pathway for the sulfonation of toluene widi sulfur trioxide.74 Intermediate 71-complcx. Wheland intermediate and pyrosulfonate species (34) are suggested, the product (p-toluenesulfonic acid) arising from an exothermic reaction between toluene and the acid (35) fonned by a facile prototropic rearrangement of (34). The sulfur trioxide monosulfonation of isopyrene and some derivatives leads usually to sulfonated... 

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