Reductive ring opening of dihydrodibenzothiepine and dihydrodinaphtho-oxepine and -thiepine

The 4,4′di-tert-butylbiphenyl (DTBB)-catalysed lithiation of dihydrodibenzothiepine () at −78 °C for 30 min followed by reaction with a carbonyl compound [tBuCHO, Ph(CH2)2CHO, PhCHO, (n-C5H11)2CO, (CH2)5CO, (CH2)7CO, (−)-menthone] at the same temperature leads, after hydrolysis with 3 M hydrochloric acid, to sulphanyl alcohols . If after addition of a carbonyl compound as the first electrophile [Me2CO, (CH2)5CO, (−)-menthone], the resulting dianion of type is allowed to react at room temperature for 30 min, a second lithiation takes place to give an intermediate of type , which by reaction with a second electrophile [Me2CO, Et2CO, (CH2)5CO, ClCO2Et], yields, after hydrolysis, difunctionalised byphenyls . The cyclisation of the sulphanyl alcohol under acidic conditions yields the eight-membered sulphur containing heterocycle . The lithiation of dihydrodinaphthoheteroepines and with 2.2 equiv of lithium naphthalenide in THF at −78 °C followed by reaction with different electrophiles [H2O, D2O, tBuCHO, Me2CO, Et2CO, (CH2)4CO, (CH2)5CO] at the same temperature leads, after hydrolysis, to unsymmetrically 2,2′-disubstituted binaphthyls and , respectively. When the lithiation is performed with an excess of lithium in the presence of a catalytic amount of DTBB (10% molar), a double reductive cleavage takes place to give the dianionic intermediate , which by reaction with different electrophiles [H2O, Me2CO, Et2CO, (CH2)4CO, (CH2)5CO], followed by hydrolysis with water, yields symmetrically 2,2′-disubstituted binaphthyls and . In the case of starting from (R)- or (S)-dihydrodinaphthoheteroepines and , these methodologies allow us to prepare enantiomerically pure compounds , and .