54815-42-8Relevant articles and documents
Stereoselective intramolecular cyclization of β-alkoxycarbonyl-ω-formylallylsilanes into bicyclic α-methylene-γ-lactones
Nishitani,Nakamura,Orii,Arai,Yamakawa
, p. 822 - 831 (2007/10/02)
α-Methylene-γ-lactones fused to five- and six-membered carbocycles were efficiently synthesized from β-ethoxycarbonyl-ω-formylallylsilane derivatives by means of the intramolecular Hosomi reaction. The formylated allylsilanes (11a, b, 12a and b) were synthesized from ethyl β-trimethylsilylpropionate and ω-tetrahydropyranyloxypentanal (4a) and -hexanal (4b) in several steps. The cyclization reaction of these aldehydes was performed under mild conditions with a high degree of stereocontrol. Treatment of the (E)- and (Z)-isomers of the allylsilanes (11a and 12a) with titanium tetrachloride or boron trifluoride etherate gave a five-membered cis-hydroxy ester (13a). Treatment of the (Z)-allylsilane derivative (11b) with titanium tetrachloride afforded a six-membered cis-hydroxy ester (13b) as a major product together with the trans-isomer (14b), and treatment with boron trifluoride etherate selectively gave the cis-isomer (13b). On the other hand, treatment of (E)-allylsilane (12b) with titanium tetrachloride selectively gave the cis-hydroxy ester (13b), while the use of boron trifluoride etherate exclusively afforded the trans-isomer (14b). These stereoselectivities can be explained in terms of chelated transition models. Lactonization of these hydroxy esters afforded the corresponding fused α-methylene-γ-lactones (16a, 17a and b) in good yields.
Bis Heteroannulation. 4. Facile Syntheses of Methylene Acids, Methylbutenolides, α-Methyl-γ-lactones, and Related Materials. Total Syntheses of (+/-)-Ligularone and (+/-)-Petasalbine
Jacobi, Peter A.,Craig, Todd A.,Walker, Donald G.,Arrick, Bradley A.,Frechette, Roger F.
, p. 5585 - 5594 (2007/10/02)
Acetylenic oxazoles of proper design undergo and intramolecular Diels-Alder reaction leading directly to fused ring furan derivatives ("bis heteroannulation").With 5-ethoxyoxazoles the corresponding 2-ethoxyfurans are obtained, and these latter materials are excellent precursors for methylene esters, methylene acids, methylbutenolides, α-methyl-γ-lactones, and β-methylfurans.In similar fashion, acetylenic oxazoles unsubstituted in the 2-position have been utilized for highly efficient syntheses of (+/-)-ligularone and (+/-)-petasalbine.
