FORMATION OF 3-MEMBERED RINGS BY S(H)I DISPLACEMENT - REVERSE OF CYCLOPROPYL RING-OPENING

The general methods, photoinitiated or peroxide-initiated free radical chain additions of halomethanes to olefins, yield 1,2-addition produc es at temperatures ranging from 20 to 100 degrees C. At lower temperat ures, -42 to -104 degrees C, a competitive reaction, subsequent to the addition of CCl(2)X, yields alkylcyclopropanes. The reactions of 1-oc tene or 1-hexene and 1-methylcyclohexene with atomic hydrogen carried out in the presence of several transfer agents (CCl4, CCl3Br, CCl2Br2) initiate a radical chain addition of CCl(2)X(.) and yield cyclized ma terials resulting from the S(H)i displacement of halogen by a carbon-c entered radical. The radical displacement of a halogen on carbon, the reverse of homolytic displacement on cgclopropyl carbon, is dominant a t low temperatures. The rate constants for cyclization (k(c)) vs trans fer with halomethane (k(t)) showed isokinetic temperatures of -46 degr ees C (CCl4, 1-hexene); -35 degrees C (CCl4, 1-methylcyclohexene). The isokinetic temperatures for the reactions of the two substrates carri ed out in the presence of BrCCl3 were calculated as -204 degrees C (1- octene) and -109 degrees C (1-methylcyclohexene).