Twisted amides: synthesis and structure of 1,6-dipivaloyl-3,4,7,8- tetramethyl-2,5-dithioglycoluril.

[structure: see text] The 1,6-dipivaloyl derivative of 3,4,7,8-tetramethyl-2,5-dithioglycoluril (6) was prepared and the crystal structure determined by X-ray diffraction; 6 is a twisted amide in which severe ring strain and nonbonded interactions compel both pivaloyl groups to twist dramatically out of the ring plane. The amide oxygen atoms point in opposite directions with respect to the mean plane through the glycoluril core, and the bridgehead methyl groups are forced out of the symmetric syn geometry (eta = 30.5 degrees ). The structure of 7, a rearrangement product generated during synthesis of 6, was also determined by single-crystal X-ray diffraction.