4,5-DIFORMYL-1,3-DITHIOL-2-YLIDENE SUBSTITUTED ETHANALS OR ETHANONES AND VINYLOGS OF TETRAFORMYLTETRATHIAFULVALENE FROM ACETYLENEDICARBALDEHYDE AND 3-THIOXO-1,2-DITHIOLES

The cycloaddition of 3-thioxo-1,2-dithioles onto mono-(diEt)-acetal of acetylenedicarbaldehyde gives stable thials or thiones 5'. The thials are readily converted into 2 by dimerization with loss of sulfur, and the trans-configuration at the central C=C bond is demonstrated by UV-visible spectroscopy. For thiones or thials 5('), the conversion of the C=S to C=O group with mercuric acetate-acetic acid leads to trialdehydes 1. The X-ray structure and spectroscopic studies reveal a delta-cis conformation in all our X=S or X=O compounds due to S ... S or S ... O 1,5-interactions.