Empirical and theoretical fusion barriers for1H and4He: Connections to evaporation from hot nuclei

Fusion excitation functions for¹H and⁴He have been compared to a one-dimensional, barrier-penetration model. In contrast to fusion for heavier nuclei this simple model is completely adequate, except for the statically deformed targed²³³U. Empirical barrier heights are obtained and compared to those from two theoretical nuclear potentials. These empirical barriers (from cold reactants) are used as input for calculating evaporation spectra that arise from hot nuclear emitters. The excess of observed low-energy¹H and⁴He emission signals information content concerning distortions of the hot nuclei.     

The molecular and crystal structure of endo-2-methyl-7-hydroxy-7-oxo-N-phenyl-7-phosphabicyclo-[2.2.1] hept-2-ene-5,6-dicarboximide

The structure of the title compound1 has been determined by X-ray crystallography analysis. The following crystal data were found: orthorhombic,Pca2_l,a=9.60691),b=16.356(1),c=8.686(1) . Both the phospholane and phospholene rings involved in the 7-phosphabicyclo-[2.2.1] hept-2-ene system have almost regular envelope conformations, and the cyclohexene ring has a significantly deformed boat conformation. The low value of the C–P–C angle, 84.2(2)°, reflects the steric strain around the phosphorus bridge and may be responsible for the reactivity of esters and amides derived from1 in the O-insertion reaction with m-chloro-perbenzoic acid. The dihedral angle between the plane of the benzene and succinimide rings is 82.4(2)°.     

Photochemical Reaction between Tertiary Allylic Amines and Chromium Carbene Complexes: Synthesis of Lactams via a Zwitterion Aza Cope Rearrangement

Photolysis of chromium carbene complexes in the presence of tertiary allylic amines resulted in a zwitterionic aza Cope rearrangement to produce unsaturated lactams in fair yield.     

Synthesis of trans-3,4-Dimethyl-4-(3-hydroxyphenyl)piperidine Opioid Antagonists: Application of the Cis-Thermal Elimination of Carbonates to Alkaloid Synthesis

Improved syntheses of twotrans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine opioid antagonists from 1,3-dimethyl-4-piperidinone are described. The 1,3-dimethyl-4-arylpiperidinol 23 was selectively dehydrated in a two step process to the 1,3-dimethyl-4-aryl-1,2,3,6-tetrahydropyridine 26 by the cis-thermal elimination of the corresponding alkyl carbonate derivative at 190 degrees C. In the presence of a basic nitrogen, the success of the elimination was found to be critically dependent upon the nature of the carbonate alkyl group, with Et, i-Bu, and i-Pr being preferred (90% yield). Alkylation of the metalloenamine, formed by deprotonation of 26 with n-BuLi, proceeded regio- and stereospecifically to give the trans-3,4-dimethyl-4-aryl-1,2,3,4-tetrahydropyridine 27, which was converted in three steps to the common intermediate, (3R,4R)-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine. LY255582, a centrally-active opioid antagonist, and LY246736-dihydrate, a peripherally-active opioid antagonist, were prepared from 1,3-dimethyl-4-piperidinone in 11.8% yield (8 steps) and 6.2% yield (12 steps), respectively.