2-Chloro-1,4-benzodithiin 1,1,4,4-Tetraoxide – A Conjunctive Dienophile for the Preparation of Tetrasubstituted Polycyclic Olefins

Abstract

2‐Chloro‐1,4‐benzodithiin 1,1,4,4‐tetraoxide 11 is a reactive dienophile that forms Diels‐Alder adducts with a number of dienes. Adducts 17a–j undergo facile dehydrochlorination to give 2,3‐substituted 1,4‐benzodithiin tetraoxides 18a–j, which react further with another molecule of diene (the same or a different one) affording the “double” adducts 19‐23. Upon reductive desulfonylation with sodium amalgam, the latter are transformed to tetrasubstituted polycyclic olefins 24‐27. These olefins correspond to the cycloadducts that would theoretically have been formed by the cycloaddition of diatomic carbon with two molecules of diene, reacting in a Diels‐Alder fashion.

1,4-Dithianes: attractive C2-building blocks for the synthesis of complex molecular architectures

“…Similarly, simple imines like 48 were found to be rather effective aza-dienophiles for this electron-poor single -cis -locked diene ( Scheme 9d ). Somewhat unexpectedly, and in contrast to the results from Nakayama [ 50 ] and De Lucchi [ 33 , 53 – 54 ], the dithiin-type vinyl disulfones like 47 and 49 actually resisted all attempts to further undergo a Diels–Alder reaction with normal dienes, even for highly reactive ones like cyclopentadiene. As a conclusion, the additional benzo-ring fusion seems to be an important factor in the swift propellane-forming reactivity of dithiin-type dienophiles 7 and 27 .…”

“…The chlorinated 1,4-dithiin-derived dienophile 27 can be used as a ‘linchpin’ reagent ( Scheme 8c ), as a first Diels–Alder reaction can be followed by a straightforward base-promoted β-elimination of the chloride, releasing another reactive dienophile. This way, highly congested ring systems can be built up around the dithiin ring system, such as the C 2 -symmetrical sesquinorbornene 37 [ 33 , 53 ], but also asymmetrical congested ring systems can be accessed using this strategy. Finally, De Lucchi also designed a high yielding multistep sequence in which 27 can be used as a bench-stable alternative reagent for benzyne ( Scheme 8d ) [ 54 ].…”

[4+2] Cycloaddition Reactions Between 1,8‐Disubstituted Cyclooctatetraenes and Diazo Dienophiles: Stereoelectronic Effects, Anticancer Properties and Application to the Synthesis of 7,8‐Substituted Bicyclo[4.2.0]octa‐2,4‐dienes

“…For the unsubstituted parent compound (9, R= H) the reaction proceeds in high yield with a range of dienophiles, including singlet oxygen, [19] maleic anhydride, [18,20,21] [20,22] tetracyanoethylene, [23] [24] 4-phenyl-1,2,4-triazole-3,5-dione (PTAD, 12), [25,26] benzoquinones, [27] [28] and 1,2-benzisothiazol-3-one 1,1-dioxides. [29] A [4+2] cycloaddition between a monosubstituted cyclooctatetraene (9, R¼ 6 H) and a symmetrical dienophile could, in principle, result in four regioisomeric products, as there are four different possible regioisomers for bicycle 10.…”