<i>Allium</i> Chemistry:  Synthesis and Sigmatropic Rearrangements of Alk(en)yl 1-Propenyl Disulfide <i>S</i>-Oxides from Cut Onion and Garlic¹

Abstract

Reduction (LiAlH 4 ) of propyl 1-propynyl sulfide ( 8 ) to ( E )-1-propenyl propyl sulfide (( E )- 10 ), C−S cleavage (Li/NH 3 ) 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/NH 3 and then MeSO 2 Cl gives ( Z, Z )- 2 via Li ( Z )- 11 . Reaction of MeSO 2 SR (R = Me ( 12a ), n -Pr ( 12b ), CH 2 CH CH 2 ( 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 ), CH 2 CHCH 2 ( 3c )) from 12a − c, respectively. Oxidation at −60 °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 (±)-(1α,2α,3β,4α,5β)-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 (1α,2α,3α,4α,5β)-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 °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 NaIO 4, 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 °C 2 gives 1:1 cis - and trans -2-mercapto-3,4-dimethyl-2,3-dihydrothiophene ( 29 ).