Cyclopropanation - Carbohydrates: Tools for Stereoselective Synthesis - page 116

Table 5.8

Reaction of DAGOH with different sulfinyl chlorides.

O O

O

Base

R 1 S

+

R 1 S

R 1 S

+ DAG-OH

ODAG ODAG

Cl

THF or toluene
-78 °C

rac -33 34- S S

34- R S

Entry R 1 Base Yield a) (%) 32- R S : 32- S S

1 Me Pyridine 87 93 : 7

2 Me i -Pr 2 NEt 90

< 2 : ≥ 98

3 Et Pyridine 85 86 : 14

4 Et i -Pr 2 NEt 90

< 2 : ≥ 98

5 n -Pr Pyridine 75 85 : 15

6 n -Pr i -Pr 2 NEt 80 4 : 96

7 i -Pr Pyridine 56 ≥ 98 : < 2

8 i -Pr i -Pr 2 NEt 50 < 2 : ≥ 98

9 p -Tol Pyridine 84 86 : 14

10 p -Tol i -Pr 2 NEt 87 6 : 94

a) Diastereomerically pure compounds after purification of the major isomers by chromatography

or recrystallization.

Table 5.9 Synthesis of optically active sulfoxides, 35a-e and ent - 35a-e, from (R) - and
(S) -DAG alkane- or arene-sulfinates, 34a-e, and R 2 MgX.

Entry Sulfinate R 1 R 2 in R 2 MgX Sulfoxide Yield (%) Configuration (ee %)

1 34a (R) Me p Tol 35a 84 (R) 100

2 34a (S) Me p -Tol ent-33a 90 (S) 100

3 34b (R) Et p -Tol 35b 96 (R) 99

4 34b (S) Et p -Tol ent-33b 90 (S) 99

5 34c (R) n -Pr p -Tol 35c 88 (R) 100

6 34c (S) n -Pr p -Tol ent-33c 89 (S) 100

7 34d (R) i -Pr p -Tol 35d 98 (R) 100

8 34d (S) i -Pr p -Tol ent-33d 89 (S) 100

9 34e (R) p -Tol Et 35e 87 (S) 70

10 34e (S) p -Tol Et ent-33e 80 (R) 100

The DAG methodology has been used in the synthesis of both enantiomers of
oxisuran a synthetic immunosupressor drug [28], the antibiotic sparsomycin [29],
and the antitumoral sulforaphane [30]. Application of the DAG methodology is
not limited to chiral sulfoxides but can be used for the synthesis of other interest-
ing chiral sulfinyl derivatives. Accordingly, the addition of LiHMDS to diastereo-
merically pure sulfinate esters leads to optically pure sulfinamides [31], which are
efficient chiral auxiliaries for the synthesis of amine-containing chiral compounds
[24].