Syntheses and CD studies of 5α‐cholesteno[3,2‐ d ]‐, ‐[2,3‐ d ]‐ and ‐[3,4‐ d ]pyrimidines

Syntheses of 5α‐cholesteno[3,2‐ d ]‐ ( 5a ), [2,3‐ d ]‐ ( 12a ), and [3,4‐ d ]pyrimidines ( 15a ) have been achieved by using hydroxymethylene derivatives of relevant cholestanones prepared from cholesterol ( 1 ). Their CD spectra exhibit at least three Cotton effects between 300 to 200 nm, a first CD band around 290, a second one around 260 and a third one around 220 nm. A quadrant rule is developed and applied to the determination of the sign of the first CD band, while a helicity rule is applicable to the third CD band. The first band is positive in the [3,2‐ d ] series, whereas it is negative in the [2,3‐ d ] and the [3,4‐ d ] series. The third band is negative in all three series.