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Syntheses of the first bridgehead sultams and the only known bridgehead disulfonimide are described. Both approaches capitalize on the electrophilicity of alpha-sulfonyl radicals and their propensity to undergo intramolecular ring closure. Where double bonds are concerned, 5-exo and 6-exo pathways operate preferentially as long as structural strain is not excessive. When the reaction center is a carbon-carbon triple bond, the first cyclization gives rise to vinyl radicals that hold sufficient reactivity to capture solvent benzene. In the case of 45, this sequential reaction leads importantly to the introduction of a styrene functionality sufficiently activated to allow a second ring closure to be kinetically feasible. The solid-state structural features of 12 and 17 have been elucidated by X-ray crystallographic methods. Despite key differences from the norm in the alignment of the nitrogen lone pair relative to the adjacent sulfonyl groups, these compounds exhibit good hydrolytic stability. For 13, generation of the alpha-sulfonamide carbanion is possible and regiospecific oxidation with chromyl acetate has been achieved.

The N-(bromomethanesulfonyl) azabicyclic ketones 2a-c and their exo-methylene analogues 1a-c were prepared. Our examination of the radical-induced behavior of the latter triad provided experimental evidence for the propensity of the b and c systems to engage in 7-endo cyclization. For 1a, only reductive debromination was observed. In no instance was ring closure by the 6-exo radical mode seen. As concerns ketones 2a-c, all three showed a remarkable facility for engaging in intramolecular S(N)2 displacement in the presence of KHMDS. Yields at the mid-80% level were realized irrespective of the value of n. Molecular mechanics calculations of the Monte Carlo type were performed on several conformational isomers and product classes in an effort to provide support for the explanatory conclusions offered as rationale for the collective experimental observations.

The stereoselective synthesis, characterization, and X-ray crystal structure of a new example of a half-sandwich zirconium complex containing a nonplanar cyclopentadienyl ligand are reported. Preli...

Exo,exo derivatives of the efficient catalyst precursors (diisodicyclopentadienyl)titanium and -zirconium dichloride substituted at the central position have been synthesized. These compounds have been characterized by solution NMR measurements, which also permitted the calculation of rotational barriers. The solid-state structures of exo,exo-bis(3-diphenylphosphinoisodicyclopentadienyl)titanium and -zirconium dichloride were determined by X-ray crystallography. Unfortunately, after activation by methylalumoxane, these complexes are shown to serve as poor catalysts for the polymerization of propene.

Homoallylic alcohols have been prepared from alkenes by direct reaction of the ozonide with an allylic bromide in the presence of zinc.

Homoallylic alcohols have been prepared from alkenes by direct reaction of the ozonide with an allylic bromide in the presence of zinc.

Syntheses of the first bridgehead sultams and the only known bridgehead disulfonimide are described. Both approaches capitalize on the electrophilicity of α-sulfonyl radicals and their propensity to undergo intramolecular ring closure. Where double bonds are concerned, 5-exo and 6-exo pathways operate preferentially as long as structural strain is not excessive. When the reaction center is a carbon−carbon triple bond, the first cyclization gives rise to vinyl radicals that hold sufficient reactivity to capture solvent benzene. In the case of 45, this sequential reaction leads importantly to the introduction of a styrene functionality sufficiently activated to allow a second ring closure to be kinetically feasible. The solid-state structural features of 12 and 17 have been elucidated by X-ray crystallographic methods. Despite key differences from the norm in the alignment of the nitrogen lone pair relative to the adjacent sulfonyl groups, these compounds exhibit good hydrolytic stability. For 13, generatio...

[formula: see text] Addition of a very modest amount of lead tetraacetate (1.50 equiv relative to the amount of Grubbs catalyst) to ring-closing metathesis reaction mixtures effectively removes all colored ruthenium and phosphine impurities to deliver colories reaction products.

The exo,exo-bis(isodicyclopentadienyl)magnesium sandwich and the monomeric exo-(isodicyclopentadienyl)butylmagnesium TMEDA complex have been synthesized and characterized by 1H and 13C NMR spectroscopy in C6D6 solution. The solid-state structures were determined by X-ray crystallography. The stereoselectivity with which both moisture-sensitive compounds react with TiCl3·3THF and ZrCl4 was assessed and suitably compared to related observations recorded for alkali metal (Li+, Na+, and K+) complexes of isodicyclopentadiene.