Photocycloaddition reactions of the first stable thioaldehyde: 2,4,6-tri(tert-butyl)thiobenzaldehyde with substituted allenes

Irradiation of 2,4,6-tri-(tert,-butyl)thiobenzaldehyde $\text{1}$ with some alkoxy-, alkylthio-, and phenyl-allenes $\text{2}$$\text{a}$-$\text{i}$ gave one stereoisomer of a (2+2)-cycloadduct, viz. thietane $\text{3}$ in high yields (75–95%). Ringclosure is in agreement with MNDO-calculations.