Strained Cyclic Acetylenes, VII. Addition of Sulfur and Pyridine-N-oxide to Seven Membered Cycloalkynes

The first isolable dialkyl dithietes, 3 and 4, -which are not stabilized by strongly electron withdrawing substituents, have been prepared from sulfur and the seven membered cycloalkynes, 1 and 2, respectively.The first 2H-azepine, 9, has been synthesized by reaction of ;with pyridine-N-oxide, and its structure has been determined by an X-ray analysis.It rearranges on heating to the pyridine derivative 11.-Seven membered cycloalkynes, such as.lor;, show an enhanced reactivity in addition reactions of I,?-dienes, carbon disulfide, phenylazide, isocyanides and nitrones to the strained triple bond compared to open-chain analogs 3-5.In this paper we report the reactions of 1 and 2 with elemental sulfur, and of --1 with pyridine-N-oxide.-heating J,5,6,6-tetramethyl-l-thia-4-cy01~heptyn (1) with an e x c e s s of elemental sulfur in refluxing dimethylformamide for 20 min 3',3',6',6'tetramethyl-I I-thiacyclohepteno 14.5-c ] dithiete (3) (m.p. 91-91 .~O C ) was obtained in 77 k yield.From 3,3,6,6-tetramethyl-1-thia-4-cycloheptyne-1,ldioxide ( 2 ) the corresponding dithiete 5 (m.p. 190-190.5 OC, 51 k) can be prepared in an analogous manner.DMF refl.