Synthesis of 2,6-Diaryl-1,4-dithiin from Bis(arylethynyl) Sulfide

An effective preparation for 2,6-diaryl-1,4-dithiins (1) was accomplished by the reaction of bis(arylethynyl) sulfide (Ar-C C-S-C C-Ar) with Na2S center dot 9H(2)O. The mild and simple method showed a good selectivity, and allowed the formation of 2,6-diaryl-1,4-dithiins (1) in up to 96% yields. A plausible mechanism for the reaction was also proposed. Thus, bis(arylethynyl) sulfide reacts with S2-, leading first to intermediate B, followed by addition of S anion in B to another C C bond to afford 1. The structure of la was unambiguously determined by X-ray analysis. la exhibited a six-membered hetero ring with boat conformation. The bond lengths of C(1)-C(2) and C(1A)-C(2A) are the typical characteristic of C=C double bond. S(1)-C(2) and S(2)-C(1) are slightly shorter than general C-S single bonds, indicating a certain degree of conjugation between the lone pair on the sulfur atom and it electrons of the C=C bond. Crystal data for la: orthorhombic, Pnma space group, a=10.1330(11) angstrom, b=27.318(3) angstrom, c=5.5402(6) angstrom, alpha=90.00 degrees, beta=90.00 degrees, gamma=90.00 degrees, V=1533.6(3) angstrom(3), Z=4, rho(caled)=1.422 g/cm(3). The final deviation factor R=0.038, R-w=0.102.