Cyclization of 1,5-Dienes:  An Efficient Synthesis of β-Georgywood

Abstract

In the acid-promoted 1,5-diene cyclization of pseudo- to beta-Georgywood, the cyclization product is obtained with high selectivity in spite of an unfavorable substituent at the C(2)-position of the diene precursor. Preisomerization of the cyclohexene double bond, which occurs in the presence of Brønsted acids, is suppressed with >1 equiv of MXn-type Lewis acids, whereas RAlX2-type Lewis acids such as >2 equiv of MeAlCl2 have the additional benefit of steering the double bond of the cyclized product into the desired beta-position. Mechanistic studies revealed a crucial participation or nonparticipation of the carbonyl group in the cyclization reaction, depending on the acid family employed, and allowed finally the development of a cyclization reaction catalyzed by MeAlCl2 that can be generated in situ from precatalyst AlMe3.1.

Synthetic terpenoids in the world of fragrances: Iso E Super®is the showcase

“…In 2007, a thorough study was published by Fráter et al . disclosed of how such variations of parameters affect product formation and composition [22].…”

“…Iso E Super Plus ® ( 34 ) can undergo a third cyclisation to tetrahydrofuran 59 through compound rac - 53 [22]. …”

Purification and biochemical characterisation of a novel glutamate decarboxylase from rice bran

“…Durch Verwendung einer katalytischen Menge von in situ generiertem MeAlCl 2 oder AlMe 3 konnte die Bildung von Aluminiumabfall wesentlich verringert werden. Die Entwicklung von Methangas wurde im Vergleich zur ursprünglichen, stöchiometrischen Vorschrift minimiert, wodurch die Sicherheit des Prozesses verbessert wurde 255a. 257, 258 Bei einer neueren Variante, die auch zur Umsetzung in größerem Maßstab geeignet ist, wurde Methacrylnitril ( 464 ) als Dienophil verwendet (Schema ) 259.…”

Determination of Sudan IV in hot chilli powder with luminol/dissolved oxygen chemiluminescence system

“…The use of a catalytic amount of in situ generated MeAlCl 2 or AlMe 3 resulted in a significant reduction of aluminum waste. The evolution of gaseous methane was minimized compared to the original stoichiometric protocol, thereby improving the overall safety of the process 255a. 257, 258 A recently disclosed variant, also amenable to scale‐up, featured the use of methacrylonitrile ( 464 ) as the dienophile (Scheme ) 259.…”