Showing papers by "Harold W. Moore published in 1997"

Highly Regioselective Monothionation of Squaric and Semisquaric Acid Derivatives

Abstract: An efficient synthesis of 4-thioxocyclobut-2-enones by the action of 0.5 molar equivalents of Lawesson's reagent on the corresponding diones is reported.

An Efficient General Synthesis of Squarate Esters

Abstract: An efficient and general method for the synthesis of alkyl squarates is presented. This involves the reactions of squaric acid with the desired alcohol in the presence of an orthoformate. This was applicable for the synthesis of dimethyl-, diethyl-, diisopropyl, di-n-butyl and di-t-butyl squarates in yields ranging from 77–97%. It is a convenient and safe method that can be accomplished on a multigram scale.

Ring Expansion of 4-Alkynylcyclobutenones. Synthesis of Piperidinoquinones, Highly Substituted Dihydrophenanthridines, Benzophenanthridines, and the Naturally Occurring Pyrrolophenanthridine, Assoanine.

Abstract: New synthetic routes to a variety of N-heterocyclic quinones and hydroquinones are described. These include thermolyses of 4-hydroxy-4-[4-N-(benzenesulfonyl)-4-aza-1,6-dialkynyl]cyclobutenones to piperidinoquinones and 4-hydroxy-4-[3-(N-phenylamino)-1-propynyl]cyclobutenones to dihydrophenanthridinediols. Included in the array of products available by this method are benzophenanthridines, indolophenanthridines, isoindoloindoles, and pyrrolophenanthridines. The methodology was employed in a five-step synthesis of the alkaloid assoanine starting with dimethyl squarate and indoline. The key step in all of these transformations is the ring expansion of appropriately substituted 4-hydroxy-4-alkynylcyclobutenones. These are envisaged to undergo electrocyclic ring opening to the corresponding enynylketenes which ring close to diradical intermediates that then lead to products via either radical additions to proximal alkyne moieties or undergo homolytic aromatic substitution to appropriately placed aryl groups. T...