Pyrolytic cis Eliminations: the Pyrolysis of sec-Butyl Derivatives1

Pyrolysis of (thio)carbonates via computation analysis

The regioselective production of alkenes from (thio)carbonates was calculated by MP2/6-31G(d) method via pyrolysis processes. Four (thio)carbonates were calculated in this paper. They are S-sec-butyl O-methyl thiocarbonate (I), O-sec-butyl S-methyl thiocarbonate (II), sec-butyl methyl thioncarbonate (III), and sec-butyl methyl dithiocarbonate (IV). Thirteen potential thermolysis routes were revealed for the pyrolysis of each substance, including nine routes to produce regioselective alkenes and four rearrangement/decompose alternatives. Among nine alkene generation routes, six-membered ring transition states via a two-step mechanism required the lowest energy, while the other routes exhibited higher energy barriers. The calculation results demonstrated an alkene distribution hierarchy of 1-butene [Formula: see text] E-butene [Formula: see text] Z-butene for substances I and II, and an order of E-butene [Formula: see text] 1-butene [Formula: see text] Z-butene for substances III and IV.

A theoretical study towards thermolysis process of thionesters and thiolesters

This paper focuses on the thermal elimination of alkenes from methyl alkyl thionacetates and thiolacetates. Three alkyl groups are calculated: ethyl, isopropyl and tert-butyl. Possible elimination mechanisms are considered, including six- and four-membered ring transition states for alkene elimination, four-membered ring isomerization and a possible five-membered ring decomposition. Theoretical calculations are performed with the MP2 method and the 6-31G* basis set. Wiberg bond indices are also summarized to monitor the reaction progress.

A computational study on the thermal decomposition of di(tri)thiocarbonates

Alkyl methyl di(tri)thiocarbonates can be thermally decomposed into alkenes. In this paper, theoretical calculations were used to calculate the thermal decomposition procedures. Six compounds, including ethyl, isopropyl and [Formula: see text] dithiocarbonate and trithiocarbonate, were examined. For each decomposition, nine possible paths were considered, including the paths leading to the desired alkene products, as well as rearrangement and elimination reactions. This calculation was performed with the MP2/6-31G(d) method. Wiberg bond indices were also calculated to further reveal the reaction progress.

Theoretical studies on the pyrolysis of (Thion)carbonates

MP2/6-31G(d) was employed to investigate the theoretical calculations on the pyrolysis of alkyl methyl (thion)carbonates, where alkyl groups referred to ethyl, isopropyl and t-butyl groups. Nine possible pathways were considered for the pyrolysis of alkyl methyl thioncarbonates, while only seven possible pathways were found to pyrolyze alkyl methyl carbonates. Both of them had three pathways to generate the desired alkene products. Not only thermal elimination pathways were calculated, other possible mechanisms, such as rearrangements and nucleophilic substitutions, were also considered. The progress of the reactions was also investigated by the calculation of Wiberg bond indices at MP2/6-31G(d) level.

REGIOSELECTIVITY INVESTIGATION FOR THE PYROLYSIS OF XANTHATES: A COMPUTATIONAL STUDY

MP2/6-31+G(d,p)//MP2/6-31G(d) method was employed to investigate the pyrolyses of O -sec-butyl S -methyl xanthate (Chugeav reaction) and S -sec-butyl O -methyl xanthate, which gave regioselective products of E-butene, Z-butene and 1-butene. Both procedures were found to have 13 possible pathways, of which nine pathways would generate the alkene products. For O -sec-butyl S -methyl xanthate, the computational results indicated that the most favorable three pathways corresponded to a two-step mechanism, with the rate-determining step to be a thion sulfur atom involved six-membered ring transition states. The calculated products distribution was consistent with the experimental observations. However, for S -sec-butyl O -methyl xanthate, thiol-participated four-membered ring transition states were found to be more energetically favored than the six-membered ring transition state to produce 1-butene, which can be attributed to a larger sulfur atomic size than an oxygen atom. As the calculation result, only trace amount of 1-butene could be obtained with a major product being E-butene and Z-butene as a minority.