Diisopropyl squarate

Liebeskind and associates converted 3,4-diisopropyl squarate (97) to stannylcyclobutenedione 98 via a 1,4-addition-elimination sequence. 98 was then coupled with 2-iodothiophene to afford substituted cyclobutenedione 99 [85]. In another case, 3-lithioquinuclidin-2-ene, generated from the Shapiro reaction of 3-quinuclidinone (100), was quenched with Bu3SnCl to afford a unique enamine stannane 101. The Stille reaction of stannane 101 and 5-bromo-2-formyl-thiophene then furnished 3-thienylquinuclidine 102 [86]. 

An elegant approach to polyquinanes has recently been described by Paquette et aL1281 By means of an anionic-pericyclic domino reaction four new C-C bonds are formed in one process. First, a two-fold addition of a vinyl lithium reagent, e.g. cyclopentyl lithium to diisopropyl squarate takes... 

Diisopropyl squarate, available from the Aldrich Chemical Company, Inc., can be readily prepared from squaric acid according to the procedure reported by Liebeskind.3... 

Bromopropene Propene, 2-bromo- (8) 1-Propene, bromo- (9) (557-93-7) tert-Butyllithium Lithium, tert-butyl- (8) Lithium, (1,1-dimethylethyl)- (9) (594-19-4) Diisopropyl squarate 3-Cyclobutene-1,2-dione, 3,4-bis(1-methylethoxy)- (10) (61999-62-5)... 

POLVQUINANES PRODUCED FROM DIISOPROPYL SQUARATE VIA AN ELECTROCYCLIC CASCADE... 

By immobilizing 3-(n-butyl) 4-isopropoxy squarate instead of diisopropyl squarate, naphthalines were accessible. Thermolysis and air oxidation of this resin-bound substrate gave a 1,4-naphthoquinone derivative (Fig. 6.3). If the hydroxy function was acylat-ed first, no air oxidation was possible during thermolysis and 1,4-dihydroxynaphthalines were obtained (Fig. 6.3). Both compounds were cleaved from resin with 20% TFA in CH2C12. 

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