Sulfur compounds intramolecular cycloadditions

Regiospecilic intramolecular cycloadditions of nitrones to sulfur-substituted dienes, with 3-sulfolene precursors, has been realized (Scheme 2.217). The stereochemical outcome of these reactions is affected by the structure of the substituent (sulfide or sulfone) in the diene and by the chain length connecting the diene and nitrone (a) and (b) (see Scheme 2.211). The bicyclic products obtained from these reactions have been converted to interesting heterocyclic compounds (709). 

Condensed and other carbocyclic systems An interesting dimerization reaction was performed with cyclohexylidenemalononitrile 188. The reaction was performed in methanolic sodium methanolate and yielded the spiro compound 189. Acidic intramolecular cycloaddition of alkylidenemalononitrile 190 (with concentrated sulfuric acid) gave the naphthalene 191. 1 -Tetraloneanil 192 reacted with 179 to yield phenanthrene 193. ... 

Cycloadditions of diene intermediates derived from 3-sulfolenes have been utilized to synthesize a variety of compounds. Diels-Alder reaction of furan 202 with excess DMAD initially gave intermediate 3-sulfolene 203. Extrusion of sulfur dioxide gave diene 204 which further reacted with DMAD to give ester 205 . Similarly, 2-bromopyrrole 206 reacted with excess DMAD to give ester 207 . Finally, an intramolecular cycloaddition of the diene derived from 3-sulfolene 208 gave ketone 209 . 

The intramolecular cycloaddition reaction can serve as a complementary method to the intermolecular variant, by producing products with the opposite regiochemical preference. For example, product 50 was converted to 51 by sequential treatment with ethanol-sulfuric acid and acetyl chloride, thus producing a product with the opposite regiochemical outcome than compound 54, prepared via the direct irradiation of Af-acetyUndole (52) with ethyl pent-4-enoate (53, Scheme 12). 

The chemical behavior of heteroatom-substituted vinylcarbene complexes is similar to that of a,(3-unsaturated carbonyl compounds (Figure 2.17) [206]. It is possible to perform Michael additions [217,230], 1,4-addition of cuprates [151], additions of nucleophilic radicals [231], 1,3-dipolar cycloadditions [232,233], inter-[234-241] or intramolecular [220,242] Diels-Alder reactions, as well as Simmons-Smith- [243], sulfur ylide- [244] or diazomethane-mediated [151] cyclopropanati-ons of the vinylcarbene C-C double bond. The treatment of arylcarbene complexes with organolithium reagents ean lead via conjugate addition to substituted 1,4-cyclohexadien-6-ylidene complexes [245]. 

Several polycyclic cyclitol derivatives have been reported. The decalinic compound 221 was synthesized from 3,4,6-tri-O-acetyl-D-glucal. As shown in Scheme 33, intramolecular Diels-Alder cycloaddition of the triene set up a tricyclic hex-5-enopyranoside derivative which underwent Ferrier rearrangent with mercuric sulfate and aqueous sulfuric acid to afford 221. Exhaustive osmylation of... 

---