Sulfur as a regiochemical control element. Synthesis of 2-alkoxy(acyloxy)-3-alkyl(aryl)thiobuta-1,3-dienes

Abstract

The internal competition between substituents in the 2,3 positions of a diene-one being a sulfur and the other an oxygen substituent-is discussed. To examine this question, a general approach to 2-alkoxy(acyloxy)-3-alkyl(aryl)thiobuta-I ,3-dienes has been developed. Bromocyclobutanone undergoes displacement with sulfur nucleophiles without competing rearrangements of the benzylic acid type. These compounds have been 0-alkylated and 0-acylated to give 1 -alkoxy(acyloxy)-2alkyl(ary1)thiocyclobutenes. Thermal opening of the cyclobutenes, preferably by the technique of flash vacuum pyrolysis, gave the desired dienes normally in overall yields of 35-6770.

The Use of Bis(trimethylsilyl)acetamide and Bis (trimethylsilyl)urea for Protection and as Control Reagents in Synthesis

“…Silylation with BSA is then worth investigating. 39 It has also been shown that the charcoal carrier for tungstic acid-tributyltin chloride which is used in the catalysed hydrogen peroxide epoxidation of alkenes is improved by treatment with BSA. The decomposition of the hydrogen peroxide that is catalysed by surface hydroxyl groups is then less troublesome.…”

Selectivity: A Key to Synthetic Efficiency

“…13, the sulfur analog 17 produces the meta type of product 18 (Eq. 15) (19,20). While desulfurization methodology permits replacement of a C-S bond with a C-H bond, the sulfur substituent provides synthetic versatility, as demonstrated by its elimination to 19.…”

Thermal transformations of organic compounds of divalent sulfur

“…85 2-Alkoxy(acyloxy)-3-alkyl(aryl)thiocyclobutadienes are converted into the corresponding dienes on heating to 350 8C as the result of the cleavage of the C(1) ± C(4) bond in the rings. 86 Pyrolysis of 3,4-bis(methylthio)cyclobutene-1,2-dione at 450 8C leads to the ring opening with the formation of bis(methylthio)acetylene and CO. At 550 8C, hydrogen sulfide and methanethiol are also formed in this reaction. 87 Allyl and propargyl 1,1-dicyano-2-ethoxyvinyl sulfides undergo the Claisen rearrangement on distillation being converted into the corresponding O-ethyl thiocarboxylates 29.…”