CYCLOADDITION AND OXIDATION REACTIONS OF A STABLE THIOALDEHYDE, (2,4,6-TRI-T-BUTYL)THIOBENZALDEHYDE

The title thioaldehyde 1 undergoes [4+2] cycloaddition with 2,3-dimeth yl-1,3-butadiene at 160 degrees C and [3+2] cycloadditions with diphen ylnitrilimine and mesitonitrile oxide at room temperature. The interme diary cycloadduct with mesitonitrile oxide undergoes cycloreversion to give 2,4,6-tri-t-butylbenzaldehyde and mesityl isothiocyanate as the final products. Oxidation of 1 with m-chloroperbenzoic acid (mCPBA) an d dimethyldioxirane (9) gives a mixture of (E)- and Q-isomers of the c orresponding S-oxides (sulfines), the former and the latter being kine tically and thermodynamically controlled products, respectively. Altho ugh both (E)- and (Z)-sulfines are not further oxidized by mCPBA, the (Z)-sulfine is oxidized with 9 to give 7-oxa-8-thia-2,4, 6-tri-t-butyl bicyclo[4.3.0] nona-2,4,9-triene 8,8-dioxide and butyl-3,4-dihydro-4,4 -dimethyl-1H-2-benzothiopyran 2,2-dioxide, both of which are intramole cular cyclization products of an intermediary thioaldehyde dioxide (su lfene).