Highly Selective Synthesis of Polyfunctionalized Carbo- and Heterocycles Based on Ring Expansion of Squaric Acid Derivatives

Abstract

A new method was developed for the derivatization of squaric acid (1) by the Lewis acid-catalyzed reaction of such acid systems with unsaturated organosilanes to give 4-hydroxy-2cyclobutenones. For the ring expansion of such products, radical-and cation-mediated reactions as well as a thermal reaction were scrutinized and found to produce 2-(5H)-furanone and 4-cyclopentene-1,3-dione derivatives. Scheme 1Masatomi Ohno was born in Aichi-ken, Japan in 1944. He obtained his PhD in 1972 from Nagoya University under the direction of Professor T. Sasaki. From 1973 to 1975, he did postdoctoral research with Professor R. J. Crawford at the University of Alberta. In 1990, he became an Associate Professor of Applied Chemistry at the Graduate School of Engineering, Nagoya University. His current research interest is the chemistry of unique cyclic systems such as squaric acid, fullerene and adamantane.Yoshihiko Yamamoto was born in Aichi-ken, Japan in 1968. He obtained his PhD in 1996 from Nagoya University under the direction of Professor S. Eguchi. He joined Professor K. Itoh's group, and in 1997 became an Assistant Professor of Applied Chemistry at the Graduate School of Engineering, Nagoya University. His current research interest is the development of new synthetic strategies based on transitionmetal catalysis.

Ruthenium‐ and Rhodium‐Catalyzed Strain‐Driven Cleavage and Reconstruction of the C–C Bond

“…[53] In organic synthesis, squaric acid and its derivatives are attractive four (and three)-carbon synthons (Scheme 12). [54] Scheme 12. Oxidative addition of cyclobutenediones to transition metal complexes.…”

“…[72] In particular, Liebeskind, Moore, Paquette, and Danheiser have been very active in this area. [73] The conversion of cyclobutenediones into quinones [74] and 5-alkylidene-2-cyclopentene-1,4-diones [75] by using a stoichiometric amount of the transition metal complex to form a (maleoyl)metal intermediate has been studied in detail.…”

New Syntheses and Ring Expansion Reactions of Cyclobutenimines

“…[46] Ring Expansion Chemistry of Cyclobutenimines Significant synthetic utility of cyclobutenones 1 rests on their thermally induced 4p-electrocyclic ring opening to reactive alkenylketene [3] intermediates coupled with the subsequent 6p-electrocyclic ring closure involving appended unsaturated side chains to give ring expanded products. [2,4,54] For example, a unique synthesis of hydroquinones involves the thermolysis of 4-alkenylcyclobutenones to give initially dienylketenes, which provide the hydroquinones upon 6p-electrocyclic ring closure (Scheme 10). Although it was an open question whether cyclobutenimines would behave analogously, anticipation of such was suggested based upon previous work showing that photolysis of an iminocyclobutenone of type 21 leads to a products apparently derived from an a,b-unsaturated alkenyl ketenimine derivative (Scheme 11).…”

Synthesis of novel alkaloids using squaric acid esters

“…10 2-Methylquinoline-4-carboxylic acid (18) was synthesized in excellent yield through a Friedländer type reaction (Scheme 7). 15 The mechanism probably proceeds via isatic acid (17), is formed from base mediated ring opening of isatin (16), followed by an intermolecular condensation to form a Schiff base, usually with acetone. Cyclization of the Schiff base via Claisen condensation occurs between the benzylic carbonyl and the α-methylene of the imine intermediate.…”

“…These building blocks and have been utilized for the synthesis of many polysubstituted cyclic compounds including heterocycles. 17 Thermally induced ring-expansions of 4alkynyl-4-hydroxy-2-cyclobuten-1-ones are known to produce both 1,4benzoquinones and 5-alkylidenecyclopentenediones. 18 In general, alkylsubstituted alkynes offer clean conversion to quinones, 19 whereas TMS-alkyne, alkynes with electron-withdrawing groups or alkenyl-substituted alkynes affords only 5-membered products.…”