Pyridinium dichromate-induced 1,3-oxidative rearrangements of enynols

Metal-Mediated Oxidation of Tertiary Alcohols and Related Fragmentations

“…After its addition to the carbonyl group, the C 17 ϪC 20 bond breaks according to a Grob-type fragmentation, releasing acetic acid. The results of the labeling experiments are in accordance with this mechanism: when hydroxypregnenolone bears a trideuteriated methyl at position 21 and reaction is performed under 18 O 2 , the acetic acid produced contains three deuteriums and one 18 O atom, whereas no labelled oxygen is incorporated into dehydroepiandrosterone. Scheme 43.…”

“…Examples of oxidation of enynols with PDC resulting enynols gave upon oxidation with PDC the transposed ketone with good to excellent yields (Table 4). [18] This PDC-induced oxidative rearrangement proceeded with complete regiospecificity since it occurred only at the olefinic site. The reaction seems to be more selective with Z-substituted enynols.…”

“…[18] Prepared by addition of a lithium acetylide to an enone, the Table 4. Examples of oxidation of enynols with PDC resulting enynols gave upon oxidation with PDC the transposed ketone with good to excellent yields (Table 4).…”

Stereoselective Total Syntheses of Acutifolone A, Bisacutifolone A and B, Pinguisenol, and Isonaviculol

“…The TMS-protected propargyl alcohol derivative was treated with PCC, and the resultant yield of enone alkyne 28 produced was as per our expectation. 17 The TMS group of 28 was deprotected using K 2 CO 3 in methanol to afford terminal alkyne 29 ; further reduction of alkyne to alkene under Lindlar’s hydrogenation conditions 18 produced the desired dieneone compound 27 , which is C-4 desmethyl-acutifolone A (Scheme 5).…”

Oxidative allylic rearrangement of cycloalkenols: Formal total synthesis of enantiomerically pure trisporic acid B

“…Although steric interference was believed to be a major obstacle of this process, this factor turned out to be unimportant. It is assumed, that the transition state during [3,3]-sigmatropic rearrangement is as shown in Scheme 3 [ 23 – 24 ], where the hydroxyl group is fixed in a pseudo-axial orientation, any other orientation would cause severe steric interaction with the 3-methyl group.…”