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, and MARK UJJAINWALLA. Can. J. Chem. 58,2745Chem. 58, (1980. The reactions of benzeneselenenyl chloride, bromide, and 2,4,6-trimethylbenzeneselenenyl bromide with alkyl I ,3-disubstituted allenes in methylene chloride solution have been investigated. While kinetic data are in accord with similar rate determining transition states, exhibiting strong steric effects for all three species, the product distributions show changes in both chemoselectivity and configurational-selectivity in accord with two different types of steric interaction mechanisms during the product determining transition states. A mechanism involving rate limiting formation of alkylideneseleniranium ions and/or alkylideneepiselenuranes, followed by isomerization between the alkylideneseleniranium ions by a path not involving allylic ions, prior to the product determining transition states, is proposed. Chem. 58, 2745Chem. 58, (1980. On a etudie les reactions, dans le chlorure de methylene, des chlorure et bromure de benzeneselenyles et du bromure de trimkthyl-2,4,6 benzeneselenyle avec les allenes disubstituks par des groupements alkyles en positions 1 et 3. Bien que les donnees cinetiques soient en accord avec des etats de transition semblables, determinants la vitesse et montrant des effets stkriques importants pour les trois especes, la distribution des produits revele des variations a la fois dans la selectivite chimique et dans la selectivitk configurationnelle; ces resultats impliquent I'existence de types differents de mecanismes d'interactions stkriques pendant les Ctats de transition determinant la formation des produits. On propose un mecanisme dans lequel la vitesse de la reaction est limitke par la formation des ions alkylidenesCICniranium etlou des alkylideneepiselenuranes, comportant aussi une isomerisation des ions alkylidknesCICniranium par un processus n'impliquant pas les ions allyliques avant des etats de transition qui dkterminent la formation des produits.[Traduit par le journal]In a previous paper of this series we have reported the reactions of benzeneselenenyl chloride with a series of 1,3-disubstituted allenes (1). In all cases the phenylseleno moiety was observed to attack regiospecifically on the central allenic carbon, with the Z isomer formed preferentially or exclusively under conditions of kinetic control. Furthermore, chemoselectivity was observed in additions to unsymmetrically substituted allenes, in that the double bond with the most electrondonating and bulky substituent is preferentially attacked, the percentage of attack increasing as the electron-donating ability and bulk increases:In particular, attack on a double bond with a tert-butyl substituent appears to favour formation of the thermodynamically more stable Z alkenes. Thus attack on the double bond with a tert-butyl substituent gives an E:Z isomer ratio3 of 9:91 for 5,5-dimethyl-2,3-hexadiene, 12238 for 2,2-dimethyl-3,6heptadiene, 11 :89 for 2,2,6-trimethyl-3,Cheptadiene, and 0: 100 for 2,2,6,6-tetramethyl-3,Cheptadiene. The directing effect, with...

The reaction of benzeneselenenyl chloride with twenty-two propargyl alcohols in methylene chloride solution is reported. Products of both Markownikoff and anti-Markownikoff regiochemistry are formed in an anti stereospecific manner. The regioselectivity or specificity is found to be very dependent upon the nature of the substituents geminal to the alcoholic moiety. In general the presence of bulky substituents geminal to the alcoholic moiety tend to favour formation of the anti-Markownikoff adduct under conditions of kinetic control. The Markownikoff adducts are found to be favoured thermodynamically.

. 58, 1005 (1980). The reaction of benzeneselenenyl chloride with tetracycI0[3.2.0.0'~.0~.'3heptane (quadricyclene) yields, under conditions of kineticcontrol, adducts of both 1.3-and conjugative I ,6-addition, the latter being formed preferentially. Electrophiliccleavage of the cyclopropane ring occurs by both retention and inversion of configuration. In agreement with the known propensity for bond cleavage in this system only the C5-C6 and/or the CI-C7 bonds are broken. The rate of cyclopropane ring cleavage is found to follow second order kinetics, first order in quadricycleneand first order in selenenyl chloride; kOb, = 1850vs. 12 300drn3 mol-I s-I for bicyclo[2.2. Ilhepta-2,5-diene at 24.5"C in methylene chloride solvent. The use of nucleophilic solvents such as HOAc, CH,OH, and CH,CN gives products of solvent-incorporation, preferentially via 1,3-addition. Electrophilic additions of areneselenenyl halides benzeneselenenyl chloride with 2 substantiate (1) and pseudohalides (2) to carbon-carbon double these expectations (5); the specific rate constants and triple bonds have received considerable inter-for the reactions of 2 and the less strained olefin, est of late. No attention has, however, been de-cyclohexene, with benzeneselenenyl chloride in voted to the possible reaction of these electrophiles methylene chloride solution at 25°C being, respecwith carbon-carbon single bonds in, for example, tively, 12 400 and 272 dm3 mol-' s-I. cyclopropanes. In this article we wish to report Results the results of a detailed examination of the cyc~opropane ring cleavage of tetracyclo-The reaction of 1 with benzeneselenenyl chloride [3.2.0.02,7.04,6]heptane, 1, using benzeneselenenyl was initially studied in methylene chloride solution as the electrophilic The of at 23-25°C. The reaction is essentially instanta-1 as substrate was made from a consideration of its "eOUS, the deep red coloration the selenenyl anticipated high reactivity with selenium elec-chloride solution disappearing immediately upon trophiles. ~~~h 1 and the isomeric olefin bicycle-mixing. Immediate lH and 13C nmr analysis of the [2.2. ]]hepta-2,5-diene, 2, normally display high crude product mixture, after w 0 r k -u~~ shows the reactivity (3), presumably as a result of their large presence of four adducts 3-6 in the proporstrain energies, 78.7 and 25.6 kcal mol-', respec-tions 62:30:5:3. No evidence was found for prodtively (4). Earlier studies involving the reaction of

The observation of the magnetic nonequivalence of isopropyl methyl carbon resonances as a result of axial dissymmetry in 27 appropriately substituted allenes is reported. The magnitude of the nonequivalence Δ is more dependent upon the adjacent substituent group than upon the substituents which are bonded to the remote sp2 carbon of the allene. A mechanism based upon the transmission of substituent effects from the remote substituents to the collinear π orbitals is proposed.