Pyrolytic Studies in the Alicyclic Series

Boyd, James (1973) Pyrolytic Studies in the Alicyclic Series. PhD thesis, University of Glasgow.

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The thesis,concerned largely with pyrolytic elimination of esters through mechanisms other than the normal 1,2-route,is in three main parts: I Introduction, II Adamantanoid Series, and III Cyclohexyl-carhinyi and Decalyl Series. The Introduction first reviews a variety of mechanistic rationalisations advanced to explain data on 1,2-eliminations. In particular the Quasi-Heterolytic and Concerted mechanisms are critically compared. The author favours the latter,noting that ester pyrolysis can he related to the general Retro-Ene reaction. A literature survey (1900-1971) is made and twenty-two examples of reports of anomalous product formation on ester pyrolysis are recorded. Each is discussed. It appears that all recorded examples,other than those carried out under conditions likely to cause acid or surface catalysed rearrangement, may he explained by extensions of three, mechanisms namely: (a) - Elimination (as has been suggested for one example by Kwart; (b) 1,3-Elimination with cyclopropyl formation (suggested on poor evidence by Bunton); (c) 1,3-Elimination with 2-alkyl migration (suggested on good evidence by Bunton,though for one example only. ) The thesis which follows investigates aspects of the latter two mechanisms (a and b above) and structures derived by their application to model systems. II. Adamantanoid Series: 2-Adamantyl esters (i. e. tetracyclo-(3,3,1,1)-decyl-) e.g. 1 were chosen as a model. Pyrolysis of the acetate was unsuccessful,but the -S-methyl xanthate, toluene p-sulphonate, and methane sulphonate gave the products 2,4-dehydroadamantane 2 andprotoadamantene 3 ,predicted from mechanisms a and b above. (Yields and ratios varied,but maximum was 95% of 2 and 3 in the ratio 60; 40) Possible mechanisms are discussed. Other esters pyrolysed were 2-(8,9-dehydroadamantyl)-3,5-dinitrobenzoate 4 (the corresponding alcohol was produced by ozone treatment of 2,4-dehydroadamantane) and 10-protoadamantyl methane sulphonate 5. The former though eliminating ester failed to give identifiable products. The latter gave adamantane and an olefin thought to be A series of reactions was carried out on protoadamantene 3 namely epoxidation(and hydride reduction of the epoxides), hydroboration (and oxidation) and oxymercuration. The stereochemistry of 3 and its effect on the course of the above reactions is discussed. The europium shifted n. m. r. spectra of all four 4- and 5-protoadamantanols ,the 4- and 5-protoadamantanones, 4exo and 4endo-methyl protoadamantanols and 4endo-phenyl protoadamantanol are recorded and discussed. Configuration,conformation and C-C bond angle strain are among topics discussed in relation to information derived from the spectra. III Cyclohexylcarbinyl and Decalyl Series It had been hoped that a modification of the 1,3-elimination mechanism c above might explain the observation of (a) the reported formation of 1-methyl cyclohexene on pyrolysis of cyclohexylcarbinyl acetate 8 and apparent anti-elimination in some esters of cyclic alcohols e.g. 1-decalyl 11 (ref. 11) (see 8 and 11 with arrows over) The pyrolysis of 8 was,however,found to occur with formation of methylenecyclohexane 10 only,the product 9 only appearing through subsequent contact of 10 with acid. Pyrolysis of esters such as 11 did give A -1,9 octalin 12 but not by a 1,3-mechanism,since C9 -deuterium was eliminated. The anti-elimination product 12 does not appear to arise through isomerisation of ester or of the normal product t-A1,2-octalin. Various mechanisms are considered.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1973
Depositing User: Enlighten Team
Unique ID: glathesis:1973-78641
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:06
Last Modified: 30 Jan 2020 15:06

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