Page 251 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

6.11 HYDROLYSIS OF S F : A MECHANISTIC PUZZLE
2 2 231
An equivalent picture in terms of resonance forms is as follows:

−
S S S
S S S
− −

The above two-step reaction sequence is of unusual interest from a synthetic perspec-
tive. Note that we have converted a typically electrophilic aldehyde (carbonyl) carbon
into a nucleophilic carbanion center in the 1,3-dithiane anion. The overall process thus
accomplishes a polarity inversion or, to use the more popular German term, umpolung.
The 1,3-dithiane anion may now be reacted with a variety of electrophiles, such as alkyl
halides, epoxides, and carbonyl compounds, in what is known as the Corey–Seebach
reaction:
+ O
S E S Deprotection E
S S E (6.98)
−

REVIEW PROBLEM 6.14
Aldehydes (like carbonyl compounds in general) react with ethane-1,2-dithiol to yield
a 1,3-dithiolane, as shown below:

O
S
SH HCI(g)
+ R
R H SH CHCI 3
S
1,3-Dithiolane

1,3-Dithiolanes, however, are rarely used in the Corey–Seebach reaction because
anions derived from them undergo fragmentation via a pericyclic pathway, producing
ethylene as one of the products. Use arrow pushing to explain this process.

6.11* HYDROLYSIS OF S F : A MECHANISTIC PUZZLE
2 2
Sulfur forms two stable fluorides—SF and SF . Of the two, SF is exceedingly stable,
4
6
6
to the point of inertness. By contrast, SF is reactive and is used as a fluorinating agent in
4
organic chemistry. In this section, we will focus on a less known sulfur fluoride, S F , not
2 2
because of its inherent importance but because of the complexity of its alkaline hydrolysis,
which provides a nice test of our arrow-pushing skills.