Novel [3+2] 1,3-cycloaddition of the ionized carbonyl ylide +CH2OCH2 center dot with carbonyl compounds in the gas phase

For the first time [3 + 2] 1,3-cycloaddition of an ionized carbonyl ylide has been observed in gas phase ion-molecule reactions of (+CH2OCH2.) (1) with several carbonyl compounds. The reaction, which competes with electrophilic addition that leads to net CH2.+ transfer, occurs across the C=O double bond of acetaldehyde and several acyclic ketones yielding ionized 4,3-dialkyl-1,3-dioxolanes as unstable cycloadducts. Rapid dissociation of the nascent cycloadducts by loss of a 4-alkyl substituent as a radical leads to the observed products, that is cyclic 3-alkyl-1,3-dioxolanylium ions. Cycloaddition of 1 with cyclic ketones yields bicyclic spiro adducts, which also undergo rapid dissociation. Cyclobutanone yields ionized 1,3-dioxaspiro[4,3]octane, which dissociates exclusively by neutral ethene loss to ionized 4-methylene-1,3-dioxolane. Ionized 1,3-dioxaspiro[4,4]nonane is formed in reactions with cyclopentanone, and its rapid dissociation by loss of C3H6 and C2H5. yields the ionized 4-methylene-1,3-dioxolanylium and the 4-ethenyl-1,3-dioxolanylium product ions, respectively. A systematic study of this novel reaction and characterization of the product ions carried out via pentaquadrupole (QqQqQ) multiple stage (MS-(1) and MS3) mass spectrometric experiments provide experimental evidence for the cycloaddition mechanism. The dissociation chemistry observed for the cycloaddition products correlate well with their proposed structures and was compared to that of both isomeric and reference ions. Ab initio MP2/6-31G(d,p)//HF/6-31G(d,p) + ZPE potential energy surface diagrams for the reactions of 1 with acetone, fluoroacetone, and 1,1,1-trifluoroncetone support the operation of the two competitive reaction pathways, that is CH2.+ transfer and [3 + 2] 1,3-cyclonddition/dissociation, and show that the cycloaddition process is favored by electron-withdrawing substituents.119153550355

REDUCTION OF PHENYLKETONES BY IMMOBILIZED BAKERS-YEAST

Baker's yeast immobilized on chrysotile and montmorillonite stereoselectively reduced 1-phenyl-1,2-propanedione to the corresponding (1R,2S)-diol. The immobilized biocatalyst was also successfully used for asymmetric synthesis of 2-amino-1-phenylethanol and (R)- or (S)-1-phenyl-2-chloroethanol. The catalyst was reusable for more than 8 cycles.2219119

Intrinsic reactivity of gaseous halocarbocations toward model aromatic compounds

The gas-phase reactivity of a set of halocarbocations, +CH2X (X = Cl, Br, or 1), (+CHXX2)-X-1 (X-1, X-2 = F, Cl, or Br), and +CX3 (X = F or CI), with four prototype aromatic compounds (benzene, furan, pyrrole, and pyridine) was investigated via double- and triple-stage mass spectrometry and compared to that of the simplest +CH3 carbocation. A rich chemistry is observed, and the reaction channels are greatly influenced by the number and type of halogen substituents (X), the strength of the C-X bonds, the nature of the aromatic compound, and the relative stabilities of the carbocation products. [Ar-CH2](+), [Ar-CHX](+), or [Ar-(CXX2)-X-1](+) functionalization of the relatively inert aromatic Ar-H bonds is the main reaction channel observed. A structure-specific "methylene by hydride exchange" reaction with toluene and B3LYP/6-311G(d,p) calculations indicate that the benzylium ion and the 2-furanylmethyl cation are formed in the [Ar-CH2](+) functionalization of benzene and furan, respectively. Kinetic isotope effects for the [Ar-CHX]l functionalization using naturally occurring halogen isotopes (Cl-35/Cl-37 and Br-79/Br-81) were measured. Using halogen-mixed halocarbocations (+CHXX2)-X-1, we evaluated the intrinsic competition for either the [Ar-CHX1](+) or [Ar-CHX2](+) functionalization. In reactions with pyridine, no Ar-H functionalization occurs and either proton transfer, N-addition, or net [CH2](+.) transfer due to the loss of X* from the nascent adducts is observed. Structural characterization of product ions was performed by on-line collision-induced dissociation or ion/molecule reactions, or both, and when possible by comparison with authentic ions.108347009702