Allium chemistry: Synthesis and sigmatropic rearrangements of alk(en)yl 1-propenyl disulfide S-oxides from cut onion and garlic

Reduction (LiAlH4) of propyl 1-propynyl sulfide (8) to (E)-1-propenyl propyl sulfide ((E)-10), C-S cleavage (Li/NH3) to lithium (E)-1-propenethiolate (Li(E)-11), and reaction with MeSO(2)Cl gives (E,E)-bis(1-propenyl) disulfide ((E,E)-2); i-Bu(2)AlH reduction of 8 to (Z)-10 and reaction with Li/NH3 and then MeSO(2)Cl gives (Z,Z)-2 via Li (Z)-11. Reaction of MeSO(2)SR (R = Me (12a), n-Pr (12b), CH2CH=CH2 (12c), CH=CHMe (12d)) with K (E)-11 gives (E,Z)-2 from (Z)-12d; Li (E,Z)-11 gives alkyl (E)- and (Z)-1-propenyl disulfides (MeCH=CHSSR, R = Me (3a), n-Pr (3b), CH2=CHCH2 (3c)) from 12a-c, respectively. Oxidation at -60 degrees C of (E,E)-, (Z,Z)-, and (E,Z)-2 gives (E)-1-propenesulfinothioic acid S-(E)-1-propenyl ester ((E,E)-13, (E,E)-MeCH=CHS(O)SCH=CHMe) from (E,E)-2, (Z,Z)-13 from (Z,Z)-2, and ca. 2:1 (E,Z)-13)/(Z,E)-13 from (E,Z)-2. Warming (Z,Z)-13 gives (+/-)-(1 alpha,2 alpha,3 beta,4 alpha,5 beta)-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5-oxide (1a), endo-5-methyl-exo-6-methyl-2-oxa-3,7-dithiabicyclo[2.2.1]heptane (14a), and exo-5-methyl-endo-6-methyl-2-oxa-3,7-dithiabicyclo[2.2. 1]heptane (14b). Warming (E,E)-13 gives 14a and 14b; (E,Z)-13/(Z,E)-13 gives (1 alpha,2 alpha,3 alpha,4 alpha,5 beta)-2,3-dimethyl-5,6-dithiabicyclo[2.1.1]hexane 5-oxide (1b), exo-5-methyl-exo-6-methyl-2-oxa-3,7-dithiabicyclo[2.2.1]heptane (14c), and endo-5-methyl-endo-6-methyl-2-oxa-3,7-dithiabicyclo[2.2.1]heptane (14d). Oxidation of 3a-c gives MeCH=CHSS(O)R (4) and MeCH=CHS(O)SR (5). At -60 degrees C, m-CPBA (2 equiv) converts (E,E)-2 into (Z,Z)-d,l-2,3-dimethyl-1,4-butanedithial 1,4-dioxide (26) while (Z,Z)-2 gives meso- and d,l-26. With NaIO4, 4/5 (R = Me) gives (E)- or (Z)-12a and MeCH=CHSO(2)SMe (6a); with m-CPBA (Z)-MeS(O)CHMeCH=S+-O- (25a) forms. At 85 degrees C 2 gives 1:1 cis- and trans-2-mercapto-3,4-dimethyl-2,3-dihydrothiophene (29).