The reaction of 4,5-dihydro-2-morpholino-(2-pyrrolidino and diethyl 2,2(3H)-thiophenedicarboxylates 7 and ethyl 2-thio-
2-piperidino)-3-thiophenecarbonitriles 1-3with bis-phenecarboxylates 7a', 8, 9. The starting compounds 1-3 (ethoxycarbony1)carbenoid afforded stable dihydrothiophe-were synthesized by the reaction of 2-amino-4,5-dihydro-3-nium-1-bis(ethoxycarbony1)methylides 4-6. The recycliza-thiophenecarbonitriles with morpholine, pyrrolidine, and pition of compounds 4-6 with bases gave the corresponding peridine.In the previous paperC21, we showed that dichlorocarbene adds to the double bond of 4,5-dihydro-2-morpholino-3-f~-rancarbonitriles to form oxabicyclo[3.1 .O]hexanes, which undergo ring opening to yield 4-(2-chloro-3-cyano-2,4-pentadienoy1)morpholines. Under the same conditions, however, the reaction of 4,5-dihydro-2-morpholino-3-thiophenecarbonitrile (1 a) with dichlorocarbene gave only a tarry material. Therefore, we examined the reaction with copper bis(ethoxycarbony1)carbenoid instead of dichlorocarbene and obtained stable dihydrothiophenium-1 -bis-(ethoxycarbonyl) methylides 4-6 which undergo a recyclization in the presence of base.When a suspension of la-c, 2a-c, or 3a-c, diethyl diazomal~nate[~] and copper powder in toluene was heated at 100 "C, the 3-cyano-4,5-dihydrothiophenium-1 -bis(ethoxycarbony1)methylides 4a-c, 5a-c, or 6a-c were obtained in fair to good yield. 2-Thiabicyclo[3.1 .O]hexane derivatives, formed by addition of the carbenoid to the double bond of the 4,5-dihydro-3-thiophenecarbonitriles, could not be observed. The structures of 4, 5, and 6 were determined on the basis of elemental analysis and spectral data (see Experimental). The starting compounds la-3a and lc-3c had been prepared by reaction of 2-amino-4,5-dihydro-3-thiophenecarb~nitrile[~I with morpholine and piperidine in the presence of trimethylamine hydrochloride in pyridine, or compounds lb-3b with pyrrolidine in the presence of acetic acid in pyridine.One of the interesting properties of sulfonium ylides bearing P-hydrogen atoms is their susceptibility to thermal cleavage of the sulfur-carbon bond to give p-elimination However, in the thermal decomposition of cyclic sulfonium ylides such as tetrahydrothiophenium-1 -bis(methoxycarbonyl)methylide, the expected p-elimination products were not obtainedrS]. In fact, when 4a, a cyclic sulfonium ylide bearing P-hydrogen atoms, was heated at 150°C for 5 h, only starting material was recovered unchanged. Therefore, we examined the p-elimination reaction of 4-6 with a base. When compound 4a was allowed to react with potassium tert-butoxide in tert-butyl alcohol at room temp. for 2 h