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.