Introduction fragmentation scheme

Specifically, one difficulty in reviewing Cl mass spectral work is the separation of Cl-induced fragmentation from that due to pyrolysis, a variable which is highly dependent upon the method of sample introduction. This factor is frequently overlooked, and fragmentation schemes have been proposed with all ions originating from the adduct or protonated molecular ion (74MI2 82AC2456). 

Our analysis of the changes in the SC wavefunction along the reaction path strongly suggests that the two n bonds on the butadiene fragment and the ethene ti bond break simultaneously, and that the formation of the two new a bonds that close the cyclohexene ring and of the cyclohexene n bond also takes place almost in parallel. If we wish to express all of this using full- or half-arrows, it would be most appropriate to use half-arrows, as in scheme B from the Introduction ... 

With an improved synthesis of the triazole fragment in hand, which would allow for its introduction much earher in the synthesis, we started searching for a direct preparation of the P-keto amide intermediate from trifluorophenylacetic acid (9). This type of transformation has been accomplished in the past using acyl Mel-drum s acid adducts [16]. This methodology involves reaction of Meldrum s acid with activated carboxyhc acids followed by decarboxylation in the presence of nucleophiles such as alcohols or amines (Scheme 5.13). The abihty of readily avail-... 

The electron impact mass spectrum of vitamin D3 obtained with a CEC Model 21-110B instrument (Consolidated Electrodynamics Corporation, Pasadena, CA) by direct probe sample introduction is shown in Figure 5 (22). It shows a strong molecular ion at m/z 384 and a fragmentation pattern characteristic of vitamins D2 and D3, their primary metabolites and other chemically related compounds. The fragment ion assignment is shown in Scheme III (22). 

Heating thiamine disulfide (445) in triethylamine yields the A4-thiazoline-2-thione (446) as the main product. The reaction is probably initiated by the nucleophilic scission of the disulfide bond followed by liberation from one of the fragments of the sulfur which is responsible for the introduction of the thione group at the 2-position (Scheme 254) (68JCS(C)2871>. 

---