Intramolecular cyclisation of (Z)-N-4-alkenylnitrones and the effects of alkenyl substituents
作者:William P. Hems、Choon-Hong Tan、Thomas Stork、Neil Feeder、Andrew B. Holmes
DOI:10.1016/s0040-4039(98)02617-3
日期:1999.2
The intramolecular 1,3-dipolar cycloadditionreactions of (Z)-N-4-alkenylnitrones carrying various alkenyl substituents were investigated, and the regiochemistry of the resulting isoxazolidines was determined. Silyl- and bromo-substituents were found to effect significant regiocontrol on the intramolecular nitrone dipolar cycloadditionreaction.
1-Bromo-2-ethoxycyclopropyllithium: A Synthetic Equivalent of 2-Lithio-or 3-Lithiopropenal. Application to the Synthesis of Juvenile Hormone (JH-II), β-Sinensal, and Jasmonoids
resulting lithium carbenoid 3 was allowed to react with various electrophiles to give 1-substituted trans-1-bromo-2-ethoxycyclopropanes (1) in good yields. The trans relationship of Br and OEt groups was found particularly pertinent to the ethanolysis of 1 producing 2-substituted propenal diethyl acetal derivatives. The reaction has been applied to 1-methoxycyclohexene–dibromocarbene adducts, giving
A new, general synthetic approach to enantiopure α-amino ketones and syn-β-amino alcohols is described which employs the doubly chiral N-protected α-amino alkyllithiums generated via Pearson's transmetalative protocol as the key synthetic intermediates.