The Preparation and Chemistry of Oxythio and Dithiocarbenes

Abstract

<p> The chemistry of a variety of new oxythiocarbenes 33a-d, generated upon thermolyses of oxythiooxadiazolines 31a-d in solution, was studied. </p> <p> Oxadiazolines 31a-d were prepared by a substitution of the acetoxy substituent of oxadiazoline 13 with appropriate mercaptans. These oxadiazolines were found to form the corresponding oxythiocarbenes 33a-d upon thermolysis at about 60-70°C. The thermolysis temperature is about 30-40°c lower than that of dioxyoxadiazolines. The first order rate constants for decomposition of 31a-c in benzene at 60°C were determined to be approximately (2.04-2.09) x w-s s-1, which is about the same as that of dioxyoxadiazolines at 100 °C. </p> <p> In order to demonstrate the existence of the reactive intermediates 33a-d, several carbene traps were used. The formation of some interesting compounds from such trapping illustrates the synthetic utility of these carbenes. The reactions of 33a-d were compared to those of the corresponding dioxycarbenes. </p> (see diagram in text) <p> A method for preparation of 2-acetoxy-2-ethylthio-5,5-dimethyl-Δ3 -1,3,4- oxadiazoline (53), which is the sulfur analogue of 13, was developed. </p> <p> This oxadiazoline was also found to form the corresponding carbene (acetoxyethylthiocarbene) upon thermolysis in solution. In the absence of any carbene trap, the carbene underwent a 1,2-acetyl shift. The first order rate constant for decomposition of 53 in benzene at 60°c was determined to be 4.19 x 10-5 s-1. </p> <p> This oxadiazoline can lead to the syntheses of various dithiooxadiazolines (e.g. 61) by substitution of the acetoxy group. These intermediates can potentially serve as precursors to the corresponding dithiocarbenes, such as 60. </p> (see diagram in text).