Stereocontrolled synthesis of complicated oxacyclic compounds via platinum-catalyzed [4 + 2]-cycloadditions and annulations of enynals with allylic alcohols.

We report stereoselective synthesis of tricyclic ketals through Pt(II)-catalyzed [4 + 2]-cycloaddition of benzopyrilium/1-en-3-ol functionalities. For nonaromatic enynals, we obtained distinct tricyclic oxacyclic ketones due to occurrence of a new annulation reaction. This work reports the first example that [4 + 2]-cycloadducts are successfully intercepted from such functionalities in diversified approaches. The value of such cycloadditions and annulations are shown by their high diastereoselectivities and chemoselectivities.

Gold-catalyzed [4+3]-annulation of oxabicyclic benzenes with 2-substituted allylsilanes through tandem allylation and cyclization.

This work reports new gold-catalyzed [4+3]-annulations of oxacyclic benzenes with 2-substituted allylsilanes through tandem allylation and cyclization; on the basis of experimental observations, we propose a mechanism involving the opening of the oxacyclic ring by a PPh3Au+-assisted SN2-attack of allylsilanes.

Gold-catalyzed isomerization of unactivated allenes into 1,3-dienes under ambient conditions.

We have developed a gold-catalyzed isomerization of unactivated allenes into 1,3-dienes with nitrosobenzene as an additive. This reaction proceeded almost exclusively at room temperature for highly substituted allenes. The utility of this reaction is manifested by the development of one-pot [4+2]-cycloaddition of allenes and reactive alkenes.

Distinct chemoselectivities in the platinum-catalyzed 1,2-carboalkoxylations of 5-alkoxypent-1-yn-3-ol derivatives.

Two distinct Pt-catalyzed carboalkoxylations of alkynes are reported. The cycloisomerization of 5-alkoxypent-1-yn-3-ol derivatives 5 produces 2,6-dioxabicyclo[3.1.0]hexanes 6; the mechanism is postulated to involve a hydroxyl-triggered [3.3]-sigmatropic allyl rearrangement. As the same catalysis is extensible to their tertiary alcohol analogues 7, distinct dihydrofuranyl alcohols 8 were obtained through a [3.3]-allyl rearrangement that is not assisted by the hydroxyl group.