Use of hindered silyl ethers as protecting groups for the non-aldol aldol process.

[reaction: see text] Bulky epoxy bis-silyl ethers, e.g., 15, derived from 5-trialkylsilyloxy-2-alken-1-ols by epoxidation and silylation were treated with TMSOTf to afford non-aldol aldol rearrangement products, the 3,5-bis(silyloxy)alkanals, e.g., 16, with little to none of the corresponding tetrahydrofurans.

A world beyond hydrogen bonds? -Chalcogen-chalcogen interactions yielding tubular structures.

It is shown that tubular structures arise in the solid state through close chalcogen-chalcogen (X...X) contacts. As examples a variety of cyclic systems containing sulfur and selenium centers is presented. Common to all of them are close contacts between the chalcogen centers of neighboring stacks giving rise to a zigzag or ladder-type arrangement. In the case of cyclic systems of ring size 24-33 the resulting tubes are able to include hydrocarbons as guest molecules. For 2,7-ditelluraocta-3,5-diyne (17) the close contacts between the tellurium centers of the acyclic C(2) symmetric building blocks generate a helical arrangement in which n-hexane was included. The favored X...X contacts can be traced back to np(X)-sigma*(X[bond]C) interactions.

Self-organization of chalcogen-containing cyclic alkynes and alkenes to yield columnar structures.

Close contacts between chalcogen atoms in cyclic dienes and diynes are used to create columnar structures in the solid state. Rigid and fairly planar cycles with chalcogen centers are the preconditions for forming those columnar structures.