Comments on Standardization of Chemical Shift Values. In our previous report on the 1H NMR spectra of several of these bicyclic adducts,2 i.e., 18a and 18c, in addition to incorrect assignment of the protons H1-H4, we had some difficulty due to nonlinearity of the field on the C-60 HL. This problem was corrected and standards of known chemical shift were used to calibrate all spectra reported here.
Both 2,3,7,8-and 1,2,7,8-t e t r a c h l o r o d i benzofuran -U14C, s p e c i f i c a c t i v i t y 57 mCi/mol, have been obtained i n low y i e l d b u t a t > 98% p u r i t y Pschorr c y c l i z a t i o n o f 2-phenoxyanil i n e -U14C, c h l o r i n a t i o n of t h e r e s u l t a n t dibenzofuran and separation o f t h e t e t r a c h l o r o isomers by hplc. The lower y i e l d s obtained i n t h e Pschorr c y c l i z a t i o n o f "hot" 2-phenoxyaniline i n comparison w i t h t h e " c o l d " m a t e r i a l are postulated t o r e s u l t from enhanced homolytic r e l a t i v e t o h e t e r o l y t i c cleavage o f t h e "hot" diazonium i o n leading t o a "hot" f r e e r a d i c a l which polymerizes. The completely anomalous r e s u l t s observed i n the attempted palladium acetate-mediated c y c l i z a t i o n o f diphenyl e t h e r -U14C are l i k e w i s e i n t e r p r e t e d i n terms o f t h e i n t e r v e n t i o n o f a " h o t " f r e e r a d i c a l .
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