Description:
<jats:p><jats:bold>2‐Stannyl‐1,3‐dithianes. Preparation, Sn/Li‐Transmetallation, and Use for Cyclizations</jats:bold></jats:p><jats:p>In order to test the possibility of generating nucleophilic 2‐lithio‐1, 3‐dithiane centers in the presence of electrophilic groups in the same molecule, the stannylated dithianes <jats:bold>1</jats:bold>‐<jats:bold>3</jats:bold> were prepared or generated. Solutions of the lithio derivatives <jats:bold>2a</jats:bold> and <jats:bold>2b</jats:bold> could either be obtained by metallation of <jats:bold>1</jats:bold> with lithiumdiisopropylamide (LDA) or by transmetallation of <jats:bold>3</jats:bold> with alkyllithium reagents. Alkylations of <jats:bold>2</jats:bold> led to the alkyl‐stannyl‐dithianes <jats:bold>4</jats:bold>‐<jats:bold>7</jats:bold>. Additions of the trimethylstannylated lithiodithiane <jats:bold>2a</jats:bold> to aldehydes and ketones at low temperature led ‐ after hydrolysis ‐ to the adduct alcohols <jats:bold>8</jats:bold>; warming up to room temperature before hydrolysis furnished keten thioacetals <jats:bold>9</jats:bold> only with acetone (→ <jats:bold>9b</jats:bold>) and cyclohexanone (→ <jats:bold>9c</jats:bold>) as carbonyl component, while still the simple adducts <jats:bold>8a</jats:bold> and <jats:bold>8d</jats:bold> were isolated with benzaldehyde and cyclohexenone, respectively. Methyl benzoate and benzoic acid anhydride reacted with <jats:bold>2a</jats:bold> to produce the tin‐free derivatives <jats:bold>12</jats:bold> and <jats:bold>14</jats:bold>, respectively.</jats:p><jats:p>It is shown that the Sn/Li‐exchange at the 2‐position of dithianes <jats:bold>4</jats:bold>‐<jats:bold>7</jats:bold>, <jats:bold>15</jats:bold> and <jats:bold>16</jats:bold> takes place within minutes at −78°, whereas H/Li‐metallation does not occur at all at this temperature. <jats:italic>In situ</jats:italic> preparation of the cyclization products <jats:bold>17</jats:bold>‐<jats:bold>19</jats:bold> from halo‐epoxides is described. The overall yields of Sn/Li‐exchange (<jats:bold>3 → 2</jats:bold>), epoxyalkylation (<jats:bold>2</jats:bold> → <jats:bold>15</jats:bold> and <jats:bold>16</jats:bold>, repectively), Sn/Li‐exchange in <jats:bold>15</jats:bold>and <jats:bold>16</jats:bold>, cyclization (→ <jats:bold>17</jats:bold>–<jats:bold>19</jats:bold>) are twice as high (up to 80%) with the tributylin than with the trimethyltin derivatives. The intramolecular 1, 3 nucleophilic reaction <jats:bold>20a</jats:bold> → <jats:bold>17</jats:bold> is complete within 5 min at −78°. The total yields of cyclization products by the tin route (<jats:bold>3b</jats:bold> → <jats:bold>16</jats:bold> → <jats:bold>20b</jats:bold> → <jats:bold>18</jats:bold> + <jats:bold>19</jats:bold>) and by direct metallation (1, 3‐dithiane →<jats:bold>21b</jats:bold> → <jats:bold>20b</jats:bold> → <jats:bold>18</jats:bold> + <jats:bold>19</jats:bold>) are 63 and 30%, respectively.</jats:p>