Base-promoted addition of DMA with 1,1-diarylethylenes: application to a total synthesis of (-)-sacidumlignan B.

A base-promoted addition of DMA (N,N-dimethylacetamide) to 1,1-diarylethylenes has been developed, and it provides a new strategy for the synthesis of N,N-dimethyl-4,4-diarylbutanamides from 1,1-diarylethylenes at room temperature. This method allows us to achieve the goal of synthesizing (-)-sacidumlignan B, and provides simple operation and broad substrate scope by avoiding the use of transition metal catalysts.

Collective synthesis of several 2,7'-cyclolignans and their correlation by chemical transformations.

Collective synthesis of anti-malarial 2,7'-cyclolignans has been stereoselectively achieved employing (±)-cyclogalgravin (2) as a linchpin through a series of functional group conversions, including redox reactions. Interestingly, 2 can be correlated with the neolignan (±)-kadangustin J (1) isolated from a different plant source, through a highly efficient dehydrative cyclization reaction with excellent diastereotopic differentiation of the veratryl group and concomitant construction of the C1­C7 bond. It is noteworthy that the first total synthesis of stereodivergent (±)-8,8'-epi-aristoligone (5), (±)-8'-epi-aristoligone (7), (±)-8'-epi-8-OH-aristoligone (8) and (±)-8'-epi-aristoligol (9) was demonstrated.

Total synthesis of (±)-sacidumlignans D and A through Ueno-Stork radical cyclization reaction.

Efficient synthesis of (±)-sacidumlignan D (4) has been successfully achieved employing Ueno-Stork radical cyclization of α-bromo acetal 21 as a key step. Two synthetic approaches for the symmetrical diaryl ketone 19 have been discussed in detail. Notably, sacidumlignan A (1) can be also efficiently synthesized in only 7 steps with 25% overall yield, where acid triggered tandem reaction starting from analogous Ueno-Stork cyclization product 27 played an important role. Moreover, potentially biomimetic conversion from (±)-sacidumlignan D (4) to sacidumlignan A (1) could be realized.