| Record 4030 View: Overview | Glossary HistCite Guide |
|
Author(s): BELLUCCI G; CHIAPPE C; MARIONI F; MARCHETTI F
Title: FACTORS AFFECTING THE REVERSIBILITY OF THE ELECTROPHILIC STEP IN OLEFIN BROMINATION - THE CASE OF 5H-DIBENZO [A, D] CYCLOHEPTENE
Source: JOURNAL OF PHYSICAL ORGANIC CHEMISTRY 4 (6): 387-398
Date: 1991 JUN
Document Type: Journal : Article
Language: English
Comment:
Address: UNIV PISA,DIPARTIMENTO CHIM & CHIM IND,I-56100 PISA,ITALY.
Reprint: BELLUCCI, G, UNIV PISA,DIPARTIMENTO CHIM BIOORGAN,VIA BONANNO 33,I-
56100 PISA,ITALY. Abstract: The tendency of ion-pair intermediates generated by treatment of trans-10-bromo-10,11-dihydro-11-hydroxy-5H-dibenzo[a,d]cycloheptene (5) with HBr to release Br2 giving 5H-dibenzo[a,d]cycloheptene (1) has been evaluated. The observed 9:1 ratio between ion-pair collapse to the trans-dibromide (7) and Br2 release to olefin 1, as compared with the 3:7 ratio found with the 5H-dibenz[b,f]azepine-5-carbonyl chloride system, has been interpreted as indicating a much lower propensity for reversibility of ion-pair formation in the bromination of 1. The structural parameters obtained by x-ray diffraction of the dibromide 7 show for this compound an angle strain at C-10 and C-11 analogous to that found in trans-10,11-dibromo-10,11-dihydro-5H-dibenz[b,f]azepine-5-carbonyl chloride. Olefin 1 adds Br2 in 1,2-dichloroethane at 25-degrees-C according to a third-order rate law, with k3 = 30(3) M-2 s-1. About 10% of 5-bromo-5H-dibenzo[a,d]cycloheptene, arising from collapse of a dibenzo[a,d]tropylium ion intermediate (9), is formed in this reaction besides the expected trans-dibromide 7. Spectral evidence for the formation of 9, arising by rearrangement of a first formed weakly bridged ionic intermediate in the reaction of 1 with Br2, is presented. the results obtained with the 5H-dibenzo[a,d]cycloheptene system have been rationalized on the basis of the formation of very weakly bridged intermediates having a much lower tendency to revert back to olefin and Br2 with respect to the corresponding symmetrically bridged bromonium ions.
Cited References: 1974, INT TABLES XRAY CRYS, V4 ARGILE A, 1983, J ORG CHEM, V48, P209 BELLUCCI G, 1980, J AM CHEM SOC, V102, P7480 BELLUCCI G, 1985, 15 CONV NAZ DIV CHIM, P37 BELLUCCI G, 1985, J AM CHEM SOC, V107, P2464 BELLUCCI G, 1985, J ORG CHEM, V50, P3313 BELLUCCI G, 1986, J ORG CHEM, V51, P4224 BELLUCCI G, 1987, J AM CHEM SOC, V109, P515 BELLUCCI G, 1987, J MED CHEM, V30, P768 BELLUCCI G, 1988, J AM CHEM SOC, V110, P546 BELLUCCI G, 1988, TETRAHEDRON, V44, P4863 BELLUCCI G, 1989, J AM CHEM SOC, V111, P2640 BELLUCCI G, 1990, J CHEM SOC PERK T 2, P2147 BELLUCCI G, 1990, J ORG CHEM, V55, P4094 BERTI G, 1957, GAZZ CHIM ITAL, V87, P293 BROWN RS, 1984, J AM CHEM SOC, V106, P4515 BROWN RS, 1990, J AM CHEM SOC, V112, P6310 CRISTOL SJ, 1960, J AM CHEM SOC, V82, P6155 DELAMARE PBD, 1982, ELECTROPHILIC ADDITI, P136 DOERING WVE, 1954, J AM CHEM SOC, V76, P3203 DUBOIS JE, 1973, J ORG CHEM, V38, P493 FRASER RR, 1970, CAN J CHEM, V49, P746 JAFFE HH, 1962, THEORY APPLICATIONS, P450 JOHNSON CK, 1976, ORNL5138 REP KAWASHIMA K, 1978, CHEM PHARM BULL, V26, P951 NARDELLI M, 1983, COMPUT CHEM, V7, P95 OHTA T, 1984, CHEM PHARM BULL, V32, P3857 PRICE CC, 1939, J AM CHEM SOC, V61, P3390 RUASSE MF, 1972, J ORG CHEM, V37, P1770 RUASSE MF, 1974, J ORG CHEM, V39, P2441 RUASSE MF, 1978, J AM CHEM SOC, V100, P7645 RUASSE MF, 1983, J ORG CHEM, V48, P202 RUASSE MF, 1990, ACCOUNTS CHEM RES, V23, P87 RUASSE MF, 1990, J ORG CHEM, V55, P2298 SCHMID GH, 1977, CHEM DOUBLE BONDED 2, P725 SHELDRICK GM, 1976, SHELX PROGRAM CRYSTA SHELDRICK GM, 1986, SHELX 86 PROGRAM CRY SLEBOCKATILK H, 1985, J AM CHEM SOC, V107, P4504 STRATING J, 1969, J CHEM SOC CHEM COMM, P907 VYUNOV KA, 1981, RUSS CHEM REV, V50, P151 WALKER N, 1983, ACTA CRYSTALLOGR A, V39, P158 |