Patai S., Rappoport Z. 2000 The chemistry of functional groups. The chemistry of dienes and polyenes. V. 2 / 0481 544

17-Chloro-17-nitroso-3ˇ-hydroxy-5˛-androstane 213, generated from the oxime 212 of epiandrosterone and t-butyl hypochlorite, reacts with cyclohexadiene in chloroform/methanol at 20 °C to yield, after two weeks, epiandrosterone and the bridged dihydrooxazine 214 in an enantiomeric excess of better than 95%108.

Tetra-n-propylammonium periodate oxidation of the hydroxamic acids 215 (R D CH2OH, CH2OMe, CH2NHPh or CO2Me), derived from L-proline, generates nitroso compounds 216, which, in the presence of cyclohexadiene, give mixtures of diastereomeric cycloadducts 217 in 79 –89% yields and 26 –68% de values (equation 115)109.

The chiral nitroso compound 218 derived from camphor (equation 116) adds to various types of dienes to afford adducts 219–222 in high yields and excellent de values (equations 117–120)110.

Chiral dienes or chiral dienophiles or chiral Lewis acid catalysts may be involved in cycloaddition reactions. When any two of these are combined ‘double asymmetric induction’ operates111. Thus the chiral diene 223 and the optically active dienophile 224 (from D-mandelic acid) gave 225 in high de values, whereas the same diene and the enantiomeric dienophile 226 (from L-mandelic acid) — a mismatched pair — formed the diastereomeric cycloadduct 227 in only 4% de (equation 121)112.

Optically active dihydrooxazines 230 are produced by the reaction of the chiral ˛- chloronitroso compound 228 derived from D-mannofuranose with a variety of 1,3-dienes in the presence of ethanol at low temperatures via the primary adducts 229 (equation 122). Penta-1,3-diene, for instance, yields a mixture of the regioisomers 231 and 232113.

Nitrosocarbonyl-D-bornane-10,2-sultam 233 adds to cyclopentadiene to yield 234 with complete facial selectivity (equation 123)114.

cis-5,6-Diacetoxy-1,3-cyclohexadiene 235 reacts with the chiral chloronitroso compound 228 in chloroform/ethanol to give 89% of the optically active product 236 in 94% ee, four asymmetric centers having been created (equation 124). The latter was

O

Me

(231)(232)

IX. ADDITION TO S=N COMPOUNDS

N-Sulfinylarylamines react sluggishly with dienes (equation 125)116,117. N-Sulfinylsulfo- namides (from sulfonamides and thionyl chloride) are much more reactive dienophiles