Motional Narrowing of Some Stereoregular Polymethyl MethacrylatesRecent studies of stereoregular polymerization of methyl-methacrylate have revealed that the stereoregularity of this polymer from the isotactic to the syndiotactic, can be controlled by selecting suitable conditions of po1ymerization.'s2 It is interesting to note how the stereoregularity affects the physical properties of this polymer.

The 1,3-Dipolar cycloaddition of phenyl azide with 1,3,5-trimethyl-6-methylenetricyclo[3.2.1.02,7]oct-3-en-8-one occurred onto the endocyclic double bond to give the exo- and endo-adducts (7 and 8) in a similar ratio. Upon photoirradiation, 7 and 8 eliminated a nitrogen molecule to give 3,5-exo- and 3,5-endo-1,3,6-trimethyl-7-methylene-4-azatetracyclo[4.2.1.0.2,803,5]nona-9-ones (9 and 10) in good yields. The 1,3-Dipolar cycloaddition of 2,4,6-trimethylbenzonitrile oxide with 9 and 10 occurred onto the exocyclic double bond to give two stereoisomers in each case. The stereoselectivity of the reactions is discussed on the basis of the stereoelectronic factor of the aziridine ring. The thermal reaction of 9 and 10 as well as photoirradiation of 9 caused a simple C–N bond cleavage of the aziridine ring. However, photoirradiation of 10 or its dimethyl analogue caused an unusual skeletal rearrangement resulting in the formation of 9-methylene-6-phenyl-6-azatricyclo[3.3.1.02,8]nona-3-en-7-one ring system. Mechanistic pathways of the rearrangement were postulated.

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