Deshielding effect on neighbouring protons on the esterification of a hydroxyl group

Preparation and cleavage reactions of some steroidal epoxides

“…) with an authentic sample. Further elution gave 6a-dirnethoxymethyl-3P-methoxy-5a-cholestan-6~-ol (20) …”

“…C30H53N303 requires C,71.5;H,10.6;N,8.35%;M ,503.4087); vmax, (CHCI3) 3 545,3 420,3 365, and 1 696 cm-'. (b) 6a-Dimethoxymethyl-3~-methoxy-5a-cholestan-6~-01 (20) (see below) (46 mg) was heated on a steam bath for 1 h with acetic acid ( 2 ~; 5 ml) and ether (1 ml) to give, after work-up in the usual way, the aldehyde (19) (31 mg, 7579, identical (t.l.c., i.r., and n.m.r. ) with a sample prepared as described in (a).…”

“…6a-Di~zethoxymethyl-3~-methoxy-5a-cholestan-6~-ol (20).-A mixture of 6u-(1,3-dithian-2-yI)-3~-rnethoxy-5a-cholestan-6p-01 (18) (147 mg), mercury(r1) chloride (519 mg), red mercury(r1) oxide (150 mg), water (0.9 ml), and methanol (14.1 ml) was heated and stirred under reflux, under nitrogen, for 4 h. Dilute hydrochloric acid (5 ml) was added to the cooled mixture, and the suspension was stirred for 30 min and filtered. The residue was washed with methylene dichloride, and the filtrate was diluted with water and extracted with methylene dichloride.…”

“…5,6a-Epoxy-3~-methoxy-6~-methyl-5a-cholestane (28) could be obtained by dehydration of 3P-methoxy-6a-methyl5a-cholestane-5,6P-diol ( 1 5 -h o e 0 iodide or by desulphurisation, with Raney nickel, of the derived dithiane adduct (1 8). Hydrolysis of the dithiane adduct (1 8) with methyl iodide and aqueous acetone afforded the aldehyde (19) in excellent yield, whilst cleavage with mercury@) oxide and mercury(rr) chloride in aqueous methanol gave a mixture of the aldehyde (19) and its dimethyl acetal (20).…”

“…As a consequence, brief treatment of an ethereal solution of the epoxide (1 2) with boron trifluoride-diethyl ether is sufficient to induce the rearrangement indicated in Figure 2 with production, in high yield, of 5-hydroxymethyl-3P-methoxy-~-homo-~-nor-5~-cholestan-4a-one (1 6).697 In agreement with the P-hydroxy ketone structure (1 6), mild base treatment brought about a retroaldol elimination which afforded a C-5 epimeric mixture of 3~-methoxy-~-homo-~-norcholestan-4aones, from which the predominant 5P-isomer ( 17) was h o e 0 iodide or by desulphurisation, with Raney nickel, of the derived dithiane adduct (1 8). Hydrolysis of the dithiane adduct (1 8) with methyl iodide and aqueous acetone afforded the aldehyde (19) in excellent yield, whilst cleavage with mercury@) oxide and mercury(rr) chloride in aqueous methanol gave a mixture of the aldehyde (19) and its dimethyl acetal (20).…”