Alex G. Fallis

Cyclopentane synthesis and annulation: intramolecular radical cyclization of acetals

Abstract A general procedure for cyclopentane synthesis based on free-radical cyclization of thioacetals is described. This permits the rapid assembly, by intramolecular annulation, of various ring systems bearing useful functionality for use in total synthesis.

Phenylsulfenyl chloride/N,N-diisopropylethylamine: a useful reagent for cyclic ether formation (Sulfenyletherification)

Abstract A general method for the formation of cyclic ethers and lactones is described. The procedure employs phenylsulfenyl chloride and N,N-diisopropylethylamine to generate an episulfonium ion intermediate from which the cyclic products arise by internal nucleophilic displacement.

Epimerization of bicyclic vinyl tertiary-alcohols via [2,3] sigmatropic rearrangement

Abstract General methods for inverting the stereochemisty of vinyl tertiary -alcohols such as 2 and 5 into 3 and 8 respectively are described. The procedures employ a [2,3] sulfoxide rearrangement and will facilitate the extended use of the oxy-Cope rearrangement to a variety of related ring systems.

Regioselective control of allyl anions with cadmium chloride: α vs. γ condensation with aldehydes

A general method for directing the condensation of allyl anions such as 2 with aldehydes preferentially to the γ position of the unsaturated nucleophile is described. The procedure employs cadmium chloride to control the regioselectivity and will facilitate the extended use of vinylogous anions in synthesis.

Addition initiated ring closure substituted spiro[4,2]Hepta-1,3-dienes via fulvene intermediates

Abstract The reactivity of the epoxy-fulvene 1 with various nucleophiles has been examined. It is a versatile Intermediate for the preparation of spiro[4.2]hepta-1,3-diene synthons via nucleophilic addition to the C6 position followed by intramolecular cyclization of the substituted cyclopentadiene anion generated in situ.

Selective cleavage of bridged-ring cyclopropyl ketones

Abstract Reductive ring opening of the tetracyclic cyclopropyl ketones 1 to 3 is described and affords selective entry to the tricyclo[4.4.0 1,6 0 5,9 ]decane (sinularene) and to the tricyclo[5.4.0 1,7 .0 6,10 ]undecene (longifolene) skeletons.

The influence of sidechain substituents in the intramolecular Diels-Alder reaction

The intramolecular Diels-Alder reactivity of a series of methyl 5-(spiro[2.4]hepta-4,6-dien-1-yl)-2-pentenoates is described. A sidechain oxygen substituent is essential for cyclization and the 1H nmr chemical shift of the β-dienophilic hydrogen provides a useful diagnostic guide to their cycloaddition potential.

Studies in marine organic chemistry: marine natural products from invertebrates found in newfoundland waters and approaches to the total synthesis of sinularene and 12-acetoxysinularene

Abstract Our recent Studies of marine natural products, particularly steroids 1, 2, 5, 8 and 9, isolated from North Atlantic sponges and alcyonacean corals is reviewed and work in progress directed toward the synthesis of the marine sesquiterpenes, sinularene (18) and 12-acetoxysinularene (17), outlined.

A Procedure for the Facile Removal of Benzylidene Blocking Groups

Abstract Often rather complex mixtures are formed in the alkylation of unsymmetrical ketones when the enolate ion population cannot be adequately controlled. One solution to this problem utilizes a prior base condensation to introduce a suitable blocking function. Benzylidene groups have been widely used for this purpose1,2since they usually afford crystalline derivatives and their steric demands are greater than those for related procedures, permitting greater selectivity. A disadvantage, as House has pointed out3 is that “the arylidene blocking group is frequently difficult to remove after alkylation.” This difficulty has helped stimulate the development of various other blocking agents.4 Generally basic conditions alone are insufficient to remove the benzylidene function5 and the standard prooedure1