New Synthetic Methods for 6aλ⁴‐Thiapentalenes

Abstract

a six-membered ring; a 36-line spectrum would be expected for (6). The FD mass spectrum[51 also provides important evidence in favor of the four-membered ring. The peak at mje=459 corresponds to the dication of ( 4 ) , but could also be assigned to the trebly charged cation (6). The latter possibility is discounted by the appearance of the highest mass peak at m/e=917, i. e. for [K2+ -H+]+ and by the absence of ions in the range m/e= 1000-1 500. Another line at m/e = 841 arises from a cation containing one less phenyl group [Kz+ -Ph+]+. Procedure (17.4g, 41.8 mmol) in a minimal amount of CHZCIZ is slowly added dropwise PhzPCl (18.4 g, 83.6mmol) diluted with the same amount of CH2C12. After 2 h the precipitated trichlorodiphenylphosphorane is filtered off (10 g = 34 mmol = 82 %) and that remaining in solution decomposed with 1,2-epoxybutane. The solvent is distilled off in uucuo and the dry residue dissolved in CH3CN. Ether is added to the gently stirred solution until it becomes slightly turbid; precipitation is complete within 30min. The product is filtered off, washed with ether, and dried in uucuo at 40°C. Yield: 16.8g (71 %) of (2), m.p. 192°C (dec.). 'H-NMR: multiplet at 6=7.4 to 8.0ppm. 31P-NMR: two doublets at 6 = -23.63 and + 62.63 ppm; J(P,P) =42.5 Hz.( 4 ) : To a solution of (2) (8.5g, 15mmol) in CH2C12 is added solid trimorpholinophosphane (4.3 g, 15 mmol) in a single batch and the mixture is stirred at room temperature for 10 to 20min. After evaporation to dryness at 40°C the residue is taken up in benzene and the mixture filtered. The filter cake is stirred with CH2C12, whereupon (OC4HsN)3PC12 dissolves. The white residual solid is recrystallized from methanol. After washing with CHzClz it is dried at 80°C. Yield: 5.8g (79%) of (4), m.p. 385"C.-The action of bromine on the solution of ( 4 ) in CHzClz gives ( 5 ) , dec. 365"C, in quantitative yield. 31P-NMR: two triplets at 6= 14.44 and 33.64ppm; J(P,P)=7.35Hz.(2): To an ice-cooled, stirred solution of