Sequential [2+2] Photocycloaddition and Rearrangement to Substituted Cyclopentanone. A formal Synthesis of Planococcyl Acetate

An extremely short synthesis of 2,2-dimethyl-3-hydroxymethyl cyclopentanone 2 (R¹ = R² = Me), an advanced intermediate in the synthesis of the pheromone planococcyl acetate 3, is described.     

Reactions of cis-2-Boryl-1-stannylalkenes with Carbodiimides, Thiocyanates, Isothiocyanates, and Isocyanates

The reactions of (E)-2-diethylboryl-1-trimethylstannylbut-1-ene and (Z)-3-diethylboryl-2-trimethylstannylpent-2-ene with carbodiimides, methyl thiocyanate, thioisocyanates, and isocyanates were studied, and the products were characterized by multinuclear magnetic resonance spectroscopy (¹H, ¹¹B, ¹³C and ¹¹⁹Sn NMR). It was found that carbodiimides bearing tert-butyl or trimethylsilyl groups at the nitrogen atoms do not react with (E)-2-boryl-1-stannylalkenes, in contrast to dicyclohexylcarbodiimide. There was also no reaction in the case of MeSCN. All other reactions proceed via a weak NB adduct formation in the initial step, followed by different rearrangements, depending on the structure of reagents as well as on the substitution pattern at the C=C bond in alkenes. New heterocycles are formed, in which the boron atom is either tricoordinated (1,2-azaborolenes, 1,2-azaborolan! es), a nd one ethyl group has been transferred to the neighbor olefinic carbon atom, or the boron atom is tetracoordinated (1,2-azaboratoles, 1,2-oxoniaboratoles), and the trimethylstannyl group has migrated to one of the heteroatoms of the heterocumulenes.     

‘Push-Pull’ and spirobicyclic structures by reacting N-methyl cyclic ketene-N,X (X=S, O)-acetals with isocyanates and isothiocyanates

Nucleophilic N-methyl cyclic ketene-N,X (X=S, O)-acetals can react with electrophilic aryl isocyanates and aryl isothiocyanates to form ‘push-pull’ mono-adducts, di-adducts and spirobicyclic 6/5 ring compounds.