FIRST EXCLUSIVE REGIOSELECTIVE FRAGMENTATION OF PRIMARY OZONIDES CONTROLLED BY REMOTE CARBONYL GROUPS AND A NEW METHOD FOR DETERMINING THE REGIOCHEMISTRY OF CARBONYL OXIDE FORMATION

The first exclusive regioselective fragmentation of primary ozonides c ontrolled by remote carbonyl groups on ozonolysis of norbornene deriva tives and reaction of final ozonides with triethylamine as a new probe for determining the regiochemistry of carbonyl oxide formation from p rimary ozonide fragmentation are reported. Ozonolysis of the endo addu cts 3a-d and the deuterated compounds 8a and 8b in CDCl3 at -78 degree s C gave the final ozonides 4a-d, 9a, and 9b as the sole products (>95 %), respectively. No detectable amount of the isomeric final ozonides 5, 10, ii, and 12 was obtained. A mechanism is proposed to account for the exclusive regioselective fragmentation of the primary ozonides. O zonolysis of 3a-d, Ba, and 8b in CH2Cl2 at -78 degrees C followed by t reatment with triethylamine exclusively gave the convex tetraquinane o xa cage compounds 16a-d, 19a, and 19b in 85-90% yields, respectively. No detectable amount of the other regioisomers 17a-d, 20a, and 20b was obtained. Ozonolysis of 3a-d, 8a, and 8b in CH2Cl2 at -78 degrees C f ollowed by reduction with dimethyl sulfide gave the tetraacetal tetrao xa cage compounds 21a-d, 23a, and 23b in 85% yields, respectively. The difference in function between triethylamine and dimethyl sulfide in reaction with final ozonide is demonstrated. Ozonolysis of the endo ad ducts 24a and 24b in CDCl3 at -78 degrees C exclusively gave the final ozonides 27a and 27b, respectively, The order of the preference of va rious remote carbonyl groups to control the fragmentation of the prima ry ozonides formed by ozonolysis of norbornene derivatives is investig ated. Ozonolysis of the endo esters 32a-c in CH2Cl2 at -78 degrees C f ollowed by reduction with dimethyl sulfide gave the new tetraacetal ox a cages 35a-c, with an alkoxyl group directly on the skeleton, and the novel triacetal oxa cages 36b and 36c, respectively. The structures o f triacetal oxa cages are proven for the first time by X-ray analysis of the crystalline compound 36c.