Pw. Ford et al., SYNTHESIS AND STRUCTURAL-PROPERTIES OF THE BENZOPENTATHIEPINS VARACINAND ISOLISSOCLINOTOXIN-A, Journal of organic chemistry, 59(20), 1994, pp. 5955-5960
The unique pentathiepin-containing compounds varacin (1) and isolissoc
linotoxin A (3) have each been synthesized in eight steps from vanilli
n. Formation of the pentathiepin ring in varacin was accomplished by t
reatment of the dithiolate anion, generated from the Na/NH3 reduction
of bisbutyl sulfide intermediate 10, with 2 equiv of S2Cl2. Placement
of the sulfur atoms on the aromatic ring was accomplished by treatment
of 5,6-dibromovanillin (6) with cuprous n-butylmercaptide in pyridine
/quinoline at 160 degrees C. The structure of the penultimate intermed
iate, TEOC-protected varacin (II), was confirmed by X-ray diffraction
analysis. Isolissoclinotoxin A was prepared in an analogous manner, us
ing a MOM group to protect the phenol. The structure of varacin has be
en confirmed; however, reductive acetylation of 3 yielded tetraacetate
derivative 20, which was different than that reported as a product of
lissoclinotoxin A acetylation. Because the data recorded for 20 did n
ot match that previously reported, it is likely that the structure of
lissoclinotoxin A should be reassigned to regioisomer 4, which has the
phenol and methoxy group interchanged.