10.1021/ja071217x.s001
Ahmad El-Awa
Ahmad
El-Awa
Xavier Mollat du Jourdin
Xavier
Mollat du Jourdin
Philip L. Fuchs
Philip L.
Fuchs
Asymmetric Synthesis of All Eight Seven-Carbon
Dipropionate Stereotetrads
American Chemical Society
2007
yield
24. Syn methylations
diastereomeric ratios
stereotetrad
SN
2007-07-25 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Asymmetric_Synthesis_of_All_Eight_Seven_Carbon_Dipropionate_Stereotetrads/2994265
Enantiopure cycloheptadienyl sulfones <b>6</b> and <b>7</b> are diastereoselectively epoxidized to yield
epoxyvinyl sulfones <b>8</b>, <b>9</b>, <b>14</b>, and <b>16</b> in high yields and diastereomeric ratios. Syn and anti methylation of
epoxides <b>8</b>, <b>9</b>, <b>14</b>, and <b>16</b> enables access to all eight possible diastereomeric stereotetrads, seven of which
are commonly found in polypropionate natural products. Anti methylations of the above epoxides are possible
by either the reaction of methyl organometallics promoted by copper(I), or via reaction with trimethylaluminum
to yield stereotetrads <b>11</b>, <b>12</b>, <b>22</b>, and <b>24</b>. Syn methylations are achieved via Lawton S<sub>N</sub>2‘ reaction in the
case of stereotetrads <b>10, 15</b>, and <b>38</b>, while stereotetrad <b>13</b> is accessed by an oxidation/reduction alcohol
inversion sequence from stereotetrad <b>11</b>. All stereotetrads were obtained in high diastereomeric ratios and
yields, and their relative stereochemistry was confirmed by X-ray crystallography. Oxidative cleavage of
the cyclic stereotetrads yields termini-differentiated acyclic heptanyl stereotetrads ready for use in building
larger fragments in the course of target syntheses.