Dithiin to Thiophene Rearrangement

Methylation of 3-nitro-2,5-diphenyl-1,4-dithiin using a mixture of methyl iodide and silver tetrafluoroborate in methylene chloride/acetonitrile/nitromethane gave a mixture of two products in the ratio of 3 1. The major product was shown to be l-methyl-6-nitro-2,5-diphenyl-l,4-dithiinium tetrafluoroborate and the minor component to be 3-(dimethylsulphonio)-5-nitro-2,4-diphenylthiophene tetrafluoroborate. 

Give a mechanistic explanation for formation of the latter compound. 

Reaction of 4-(2-formylphenoxybutyl)triphenylphosphonium bromide with sodium ethoxide in refluxing DMF gave a mixture of 3,4-dihydro-2tf -1 -benzoxocin and 2-ethyl-2//-1 -benzopyran in the ratio 95 5 and in 31% yield. 

Suggest mechanisms to account for the formation of these products. 

Treatment of the ( -lactam 1 with N -methylhydroxylamine gave the expected condensation product, pyrolysis of which in toluene at 110°C led to formation of the isomers 2 in 72% yield. 

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