Propargylic sulfinates

A neat twofold transformation, obviously a consequence of a sigmatropic [2.3]rear-rangement rather than by an ionic pathway, occurs in the case of a propargyl sulfinate (equation 3). 

Synthetic Utility of the Propargylic Sulfinate-to-Sulfone Rearrangements. 91... 

Scheme 34 Double [2,3]sigmatropic rearrangements of bis(propargyl sulfinates)...

Propargyl sulfinate groups are exclusively substituted through an Sn2 process in a. s 7i-manner by (MeCuBr)MgCl or by (MeCuBr)MgCl-LiBr in THF, to afford the allenic derivatives 246 [81 Eq. (81)]. 

In Et20, a predominant attack on the sulfur atom in compound 243 takes place when the propargyl sulfinate 243 is treated by either an homo- or heterocuprate of the type (RCuY)MgX (Y = R or Br), leading to the formation of compounds 244 and 245. 

The reaction of tertiary propargyl sulfinate esters with (MeCuBr)MgCl or (MeCuBr)MgCl -LiBr in THF at 20 C gives rise to the formation of the allenic derivatives in 98% yield through a syn-process [81,82, Eq. (82)]. 

The same results are observed by Tadema et al. [83)]. The anr/-1,3-substitution route is the normal stereochemical pathway for secondary propargylic sulfinates, whereas the syn-route is preferred if the ester is derived from tertiary propargylic alcohols. 

Note 1. The sulfinate of propargyl alcohol did not rearrange upon heating at 130-140°C in xylene. 

Following studies on the rearrangement of allylic arenesulfinates, Braverman and coworkers have investigated a number of natural extensions of this unique transformation, including the predictable [2,3] sigma tropic rearrangements of allylic sulfenates to sulfoxides and of propargylic sulfenates and sulfinates to allenic sulfoxides and sulfones respectively. The last reaction is described below, while the other two are described in Chapter 14. 

This reaction type has been intensely studied °. The application of highly polar solvents, catalysis with tertiary amines" or with acids mesomeric stabilization of intermediate carbenium ions " (allylic and benzylic systems propargylic systems" ) as well as derivatives of sulfinic acids with increasing acidity - usually indicate an ionic pathway (intra- and/or inter-molecular) ... 

Chiral allenylstannanes can be prepared by Sjv2 displacement of propargylic halides sulfinates or sulfonates with tin cuprates (Table 14)78. The nonracemic propargylic mesylate (74) afforded a nonracemic allene, [a]D —570, whose configuration was assigned by application of Brewster s rules (equation 38)78. Displacements on the steroidal mesylates 75 and 76 afforded the allenic products with complete inversion of configuration (Scheme 32)78. 

Acid-catalyzed hydrolysis of S-allenylsulfinylamines 425, easily accessible from propargyl alcohols (cf. Scheme 7.8), provides the alkynes 427 (Scheme 7.56) [108, 109]. This transformation is postulated to proceed via the intermediate allenic sulfinic acid 426. However, in some cases with R1 = R2 = alkyl, more complicated products are formed instead of simple alkynes 427 [372]. 

Thus, the alkynyllithium derived from the propargylic ether 302 underwent allylzincation under the above-mentioned conditions and led to the dimetallic species 303. Whereas treatment with NBS resulted in the formation of the dibromoolefin 304, reaction of 303 with the less reactive benzenesulfonyl chloride produced an ce-chlorozinc sulfinate 305. The latter could in turn react with different electrophiles and afforded the corresponding tri- or tetra-substituted olefins of type 306 as single geometric isomers (equation 144)179. 

One approach to tetrahydropyridinones is the Lewis acid mediated hetero-Diels-Alder reaction of electron-rich dienes with polystyrene-bound imines (Entries 3 and 4, Table 15.23). The Ugi reaction of 5-oxo carboxylic acids and primary amines with support-bound isonitriles has been used to prepare piperidinones on insoluble supports (Entry 5, Table 15.23). Entry 6 in Table 15.23 is an example of the preparation of a 4-piperidinone by amine-induced 3-elimination of a resin-bound sulfinate followed by Michael addition of the amine to the newly generated divinyl ketone. The intramolecular Pauson-Khand reaction of propargyl(3-butenyl)amines, which yields cyclopenta[c]pyridin-6-ones, is depicted in Table 12.4. 

Scheme 27 Synthesis and [2,3]sigmatropic rearrangement of propargyl trihalomethyl sulfinates...

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