A highly convergent, enantioselective total synthesis of the aglycone of the tetrocarcins, (+)-tetronolide, is described. The synthesis highlights the use of several new methods, including camphor auxiliary-directed asymmetric alkylation and the enantioselective preparation of acyclic mixed acetals bearing chirality at the acetal center, and the highly efficient connection of the two major precursors via a ketene-trapping/intramolecular [4 + 2] cycloaddition strategy.
An enantioselective total synthesis of the apoptosis-inducing natural product, (-)-rasfonin, is described. Camphor lactam-mediated asymmetric alkylation reactions enabled the installation of three stereogenic centers with >95:5 diastereoselectivity. A modified Corey-Peterson olefination was employed in the construction of the (E,E)-diene system. A highly diastereoselective, asymmetric vinylogous Mukaiyama aldol addition was conducted using a chiral cationic oxazaborolidine catalyst. The pyranone core of the natural product was prepared via a DBU-promoted rearrangement of a furanol to its corresponding pyranol with concomitant [1,4]-silyl transfer.
[reaction--see text] Enolates of a new camphor-derived lactam auxiliary are shown to monoalkylate with very high diastereoselectivity. A second alkylation occurs with reactive alkylating agents to afford quaternary centers also with high diastereoselectivity. In accord with a proposed model for diastereoselection, lithium and sodium enolates provide products with an opposite sense of asymmetric induction.
Palladium-catalyzed coupling of an aryl siloxane and an allylic carbonate proceeded in good yield to give an adduct that was converted to an analogue of (+/-)-7-deoxypancratistatin.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Toward the Development of a General Chiral Auxiliary. Part 9. Highly Diastereoselective Alkylations and Acylations to Form Tertiary and Quaternary Centers.-Enolates containing a new camphor-derived lactam auxiliary can be alkylated and acylated with good to very high diastereoselectivity. In the case of imides (I) and (III) lithium and sodium enolates leads to products with opposite sense of asymmetric induction. -(BOECKMAN JR., ROBERT K.; BOEHMLER, DEBRA J.; MUSSELMAN, RHONDA A.; Org.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.