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to leaving group characteristics, the curvilinear form of plots such as Figures 1, 4, and 6 , the demonstration of general base catalysis, the sameness of the intercepts of inversion plots (cf. Figure 8) concerning catalysis by hydroxide ion and by piperidine, and the variation of solvent isotope effect with base concentration. Inasmuch as no conceivable alternative mechanism can accommodate these and other observations recorded in earlier papers, the evidence for this mechanism is compelling.The Mechanism of Base Catalysis. We have not discussed the question of how a base catalyzes transformation of intermediate I into products. However, this question has been discussed in previous publications.jV6' ' 5 , 38 Of several alternative mechanisms which are formally compatible with the observed kinetics, we favor one which itself comprises two steps. In the first step, intermediate I reacts reversibly with base B, losing a proton to it and forming intermediate I1 as well as the conjugate acid of the base. In the second and rate-limiting step, the conjugate acid (HB) of the footnote 26. (38) J. F. Bunnett and G. T. Davis,J. Am. Chem. Soc., 82, 665 (1960),base electrophically assists separation of leaving group X from intermediate 11. If this mechanism prevails, each knB of eq. 2 represents the product ktBK'=, where K'B is the equilibrium constant for reaction of I with base B to form I1 and HB, and k l B is the rate coefficient for HB-catalyzed expulsion of leaving group X from II. No,-The cyclization of carvone (1) to carvonecamphor (2) can be conveniently carried out using a black-light source. Continued irradiation of the carvonecamphor in alcohol or aqueous dioxane results in a photolytic cleavage, giving an ester (3 or 5) or the corresponding acid (4). Photolyses of ow-dideuteriocarvonecamphor (11) and of carvonecamphor in dioxane-deuterium oxide support the mechanism established by Quinkert for other saturated ketone photoiyJes, a mechanism involving intramolecular hydrogen transfer in an intermediate diradical. When 2 is irradiated in benzene-t-butylamine containing oxygen, the expected unsaturated acid (19) and a rearranged unsaturated acid (20) are produced, accompanied by the ketene-derived amide ( I ) . Catalytic reduction of the methyl ester of 19 gives 3 as a minor product, along with its C-5 epimer (22); chemical reduction gives chiefly 3, correlating the two types of photolysis products. The contrast between the solution photolysis of carvonecamphor and of camphor is rationalized by considering steric requirements. IntroductionThe intermolecular photochemical addition of olefins to a,P-unsaturated ketones has recently been shown to be a synthetic reaction of considerable usefulness.

Die Trihalogentriphosphabicyclo[1.1.1]pentane 2 entstehen bei der Umsetzung des 1,3‐Diphosphabicyclo[1.1.0]butan‐Komplexes 1 mit Phosphorhalogeniden. Das tricyclische Grundgerüst von 1 bleibt hier nicht erhalten, da die Reaktion unter Spaltung der P‐P‐Brücke verläuft. Der Zirconiumkomplex 1 eröffnet darüber hinaus durch gezielte Eliminierungsreaktionen einen Zugang zu bi‐ und tricyclischen Phosphorverbindungen sowie zu 1,3‐Diphosphetanen und 1,2‐Dihydro‐1,2‐diphospheten.

than in both the precursor complexes and products, see Figs. 2 and 3) compensates for the effective decrease in the coordination of lithium resulting from the partial bonding in the transition structure. The combination of these effects Scheme 1. Charge distribution in the transition state of the ortho lithiation of aromatic compounds. leads to a substantial decrease of the activation energy, and is the cause of the strong preference for ortho metalations and other regioselective metalation~.[~I This conclusion can be expected to be general. We propose "kinetically enhanced metalation" as a more appropriate designation for the accelerating effects of ortho substituents.