A hint of cassis: By a combination of microwave spectroscopy and quantum chemistry, the gas‐phase structures of the Cassyrane stereoisomers and its dihydro derivatives have been determined, and correlated with their olfactory properties. Superposition analyses of the structures (see picture; black Cassyrane, silver Oxane, red O, yellow S) reveal the importance of the 5S configuration on the cassis odor, with the 2S,5R isomers being the most intense.

Generation of radicals from B-alkylcatecholboranes represents an efficient tin-free procedure for the generation of alkyl radicals. A modified version of this method has been developed. The simple catechol is replaced by a dihydroxylated tetrahydroisoquinoline, which can be separated from the reaction products by simple extraction with an aqueous acid solution. The modified alkyl radical precursors are easily prepared from alkenes by hydroboration with BH 3 ·Me 2 S fol-

Einleitung.

The generation of 1-bromo and 1-chloroalkyl radicals from organoboranes has been investigated. The direct approach involving the hydroboration of halogenated alkenes is impeded by partial dehalogenation taking place during the hydroboration process. An indirect method involving the generation of B-(1-chloroalkyl)catecholborane by homologation of B-alkylcatecholborane with dichloromethyllithium was developed. A reaction sequence involving a hydroboration reaction, a Matteson homologation, and a radical allylation process has been performed as a one-pot process that takes advantage of three different reactivities of organoboron species. Starting from styrene derivatives, it was possible to prepare B-(1-chloro-2-arylpropyl)catecholboranes that are excellent precursors to 1-chloro-2-arylpropyl radicals. A concise approach for the synthesis of an optically active α-methylene-γ-lactone from p-chlorostyrene has been developed on the basis of a two-step sequence involving an enantioselective hydroboration-homologation-cyclization reaction followed by a hydrolysis-lactonization process.

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