[7191-32-4]  · C11H24S2Sn  · 2,2-Dibutyl-2-stanna-1,3-dithiane  · (MW 339.20)

(reagent for synthesizing 1,3-dithianes from aldehydes and acetals2,3)

Alternate Name: DSDT.

Physical Data: mp 63-64 °C; bp 170 °C/0.5 mmHg.

Solubility: insol H2O; sol most organic solvents.

Analysis of Reagent Purity: 1H NMR (CDCl3) d 0.93 (t, 6H, J = 7.32 Hz), 1.61 (m, 14H), 2.94 (t, 4H, J = 6.10 Hz); 13C NMR (CDCl3) d 13.40, 24.51, 26.50, 27.82, 30.16.

Preparative Method: to a CH2Cl2 solution (400 mL) of Bu2SnCl2 (45.8 g, 0.15 mol) and HS(CH2)3SH (15.1 mL, 0.15 mol) is added Et3N (41.8 mL, 0.3 mol) at 0 °C. The solution is stirred at rt overnight and diluted with CH2Cl2 (200 mL). The combined solution is washed with H2O (200 mL × 2). The organic layer is dried (Na2SO4) and evaporated. Distillation of the residue affords DSDT (39.5 g, 78%): bp 170 °C/0.5 mmHg.

Handling, Storage, and Precautions: stable in air and to moisture and thus can be handled and stored in air; odorless.

Synthesis of 1,3-Dithianes from Aldehydes and Acetals.2,3

Treatment of aldehydes with DSDT (1.2 equiv) in the presence of Bu2Sn(OTf)2 (DBTT) in 1,2-dichloroethane affords 1,3-dithianes in 70-99% yields (eq 1). Boron Trifluoride Etherate may also be used in this procedure; however, use of DBTT results in cleaner reactions and better yields. 1,3-Dithianes are conventionally prepared with 1,3-Propanedithiol under acidic conditions and are occasionally contaminated by yellow-colored byproducts. No such byproducts are detected in reactions with DSDT. Of more synthetic value is the mildness of the reaction. Acid-labile substrates can be successfully employed: aldehydes having siloxy or tetrahydropyranyloxy groups, which are unmasked under conventional reaction conditions, are converted to 1,3-dithianes smoothly. However, a,b-unsaturated aldehydes undergo isomerization of the double bond.

The reactions with acetals also proceed smoothly (eq 2). 1,3-Dithiolanes are obtained by an analogous procedure employing 2,2-dialkyl-2-stanna-1,3-dithiolanes in place of DSDT. In some respects this method is comparable to the Evans' thiosilane protocol,4 which, however, is applied to carbonyls only; no reaction with acetals has been described. Moreover, the following merits of the present dithioacetalization method are worthy of note. Thiostannanes can be readily prepared from various organotin sources such as oxides, alkoxides, and halides. They are entirely air and moisture stable and, thus, can be used even in the presence of water. Because they are odorless, they can be stored in the air.

Differentiation between Carbonyls and Acetals.

In competition reactions employing an equimolar mixture of various types of carbonyls and acetals, one of the substrates reacts preferentially. Representative results are described briefly in the following sections.

Competition between Aldehydes and Ketones (or Acetals).

An aldehyde reacts preferentially over a ketone (eq 3), while the preference is reversed in the reaction of the corresponding acetals (eq 4). The reaction of the carbonyl is initiated by coordination of the carbonyl to tin. Thus the enhanced reactivity of the aldehyde can be accounted for by the fact that the aldehyde forms a complex with tin more readily than the ketone does. In contrast, the reaction of the acetal proceeds via an oxocarbenium ion, which is generated from ketone acetals more easily than from aldehyde acetals.

Competition between Aldehydes.

Differentiation between two of the same type of carbonyl functions often requires highly elaborate methods. Organotin triflates effect such differentiations successfully. As shown in eq 5, competition between benzaldehyde and pentanal leads to predominant formation of the 1,3-dithiane of the latter.

Competition between Acetals.

An aromatic acetal can be differentiated from an aliphatic acetal (eq 6).

1. Poller, R. C.; Spillman, J. A. JCS(A) 1966, 1024.
2. Sato, T.; Yoshida, E.; Kobayashi, T.; Otera, J.; Nozaki, H. TL 1988, 29, 3971.
3. Sato, T.; Otera, J.; Nozaki, H. JOC 1993, 58, 4971.
4. Evans, D. A.; Truesdale, L. K.; Grimm, K. G.; Nesbitt, S. L. JACS 1977, 99, 5009.

Junzo Otera

Okayama University of Science, Japan

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