80287-85-0Relevant articles and documents
Stereospecific cyclopropanation reactions of stannyl-substituted acetals with alkenes via γ-elimination of tin
Sugawara, Masanobu,Yoshida, Jun-Ichi
, p. 1057 - 1058 (1998)
The reactions of stannyl substituted acetals with olefins resulted in the elimination of both the triorganostannyl group and the alkoxy group on the same carbon, and the production of the corresponding alkoxycyclopropanes in good yields. The stereospecifi
Reactions of Carbenes with Oxetane and with Oxetane/ Methanol Mixtures
Kirmse, Wolfgang,Lelgemann, Rudolf,Friedrich, Klaus
, p. 1853 - 1863 (2007/10/02)
Ethoxycarbonylcarbene, bis(methoxycarbonyl)carbene, phenylcarbene (17a), diphenylcarbene (17b), fluorenylidene (17c), 2-furylcarbene (31a), 2-furyl(phenyl)carbene (31b), 4-oxo-2,5-cyclohexadienylidene (40), and 4,4-dimethyl-2,5-cyclohexadienylidene (53) were generated by photolysis of the appropriate diazo compounds.With neat oxetane, most of these carbenes react by competitive C-H insertion (B -> A, Scheme 1) and ylide formation (B -> C). 31a and 40 do not insert into C-H bonds; 31b does not attack oxetane but rearranges exclusively with formation of 26.The ylides undergo Stevens rearrangement to give tetrahydrofurans (C -> D) and α',β-elimination, leading to allyl ethers (C -> E).With oxetane/ methanol mixtures, the intervention of oxonium ions (H) is indicated by the formation of 1,3-dialkoxypropanes (I).The oxonium ions arise either by protonation of the ylides (C -> H) or by protonation of the carbenes (B -> G), followed by electrophilic attack of the carbocations (G) at oxetane (G -> H).The former route is followed by the alkoxycarbonylcarbenes and by 40; the ylides derived from the remaining carbenes do not react with methanol, owing to their rapid Stevens rearrangements.Protonation of the carbenes 17b, 31, and 53 is clearly indicated by their product ratios and, for 31, by the formation of isomeric ethers (33, 36).The more electrophilic carbenes discriminate but slightly between oxetane and methanol while the more nucleophilic carbenes (17b, 31, 53) prefer the protic methanol strongly over the aprotic oxetane. Key Words: Carbenes/ Oxygen ylides/ Stevens rearrangement/ Oxonium ions/ Insertion, O-H/ Ylides
Effects of Substituents and Generation Methods on Insertion-Addition Selectivities of ''Arylcarbene'' in Alcohol-Olefin Binary Mixtures. Intervention of Reaction of Diazo Compounds Masquerading as Carbenes
Tomioka, Hideo,Suzuki, Shinji,Izawa, Yasuji
, p. 1047 - 1050 (2007/10/02)
A Hammett study of the insertion-addition selectivity (Ki/ka) and cyclopropanation stereoselectivity (kc/kt) of "arylcarbene" generated either photolytically or thermally in 2-propanol-ethyl vinyl ether binary mixtures showed that ρ values are highly sensitive to the generation method.Thus, plots of ki/ka and kc/kt vs. ? (?+) in the photolytic run gave ρ values of -0.96 (r = -0.96) and -0.15 (r = -0.95), respectively, whereas similar values are +1.4 (r = 0.93) and -1.1 (r = -0.96) in the thermal run.The results along with the effects of precursor, temperature, and sensitizer on the product distributions are interpreted as indicating that, while free carbene is involved in the photolytic run, the ground-state diazo compound is masquerading as carbene in its thermal reaction with the olefin.
