S-allyl derivatives

Some applications of the thio-Claisen rearrangement to the syntheses of thiocarbonyl compounds, particularly unsaturated dithiocstcrs and thionesters, and of its stereocontrol aspects are reviewed in [120]. A particularly high stereoselectivity was observed with S-allyl derivatives of P-hydroxydithioesters syn products were obtained exclusively, according to the accompanying scheme [495,496]. 

O-Allyl phosphonothionates rearrange on treatment with Pd° catalysts to the S-allyl derivatives.220 Alkyl substituents on the allyl group direct attack to the less substituted allyl terminus (equation 289). 

If the nitrogen atom at position 2 bears a substituent, alkylation proceeds at the nitrogen atom in position 4 of the thienopyrimidine system, as exemplified (1988DOK1135, 1989KGS413) by the formation of thiazolothienopyrimidinium salts 185 from S-allyl derivatives 186. 

Several of these compounds are listed in the Merck Index. The p-blocking oxprenolol, the arylacetic analgesic-anti-inflammatory drug aclofenac and the fungicide enilco-nazole are 0-aUyl derivatives. Penicillin O and penicillin S are both S-allyl derivatives. 

The first examples of an asymmetric thio-Claisen rearrangement induced by a cyclic chiral auxiUary were described by Reddy and Rajappa [127]. N-Nitrothioacetyl derivatives of (I)-aminoacid esters were used as substrates (Scheme 9.26). After allylation in the presence of DBU, the resulting S-allyl derivatives underwent facile thio-Claisen rearrangements upon heating at 50 °C but with modest chiral induction (up to 66% de). 

Stockman has reported the preparation of alkyl-, aryl-, and vinyl-disubstituted aziridines with good diastereoselectivities and in good yields through treatment of tert-butylsulfmylimines with the ylide 119, derived from S-allyl tetrahydrothio-phenium bromide (Scheme 1.39) [64]. A range of substrates were tolerated, including heterocyclic, aromatic, and aliphatic substrates (Table 1.16). 

Thia-[2,3]-Wittig sigmatropic rearrangement of lithiated carbanions 47, obtained by deprotonation of the S-allylic sulfides 46, affords the thiols 48 or their alkylated derivatives 49. The corresponding sulfonium ylides 51, prepared by deprotonation of the sulfonium salts 50 also undergoes a [2,3]-sigmatropic shift leading to the same sulfides 49 [36,38] (Scheme 13). As far as stereochemistry is concerned, with crotyl (R R =H,R =Me) and cinnamyl (R, R =H,R =Ph) derivatives, it has been shown that the diastereoselectivity depends on the nature of the R substituent and on the use of a carbanion or an ylide as intermediate. 

The allylation of thiadiazole-2-thione 114 with ally 1 bromide gave as the main product the N-allyl derivative 115 with trace amounts of the corresponding S-derivative 116 (Equation 36) <2003CHE228>. Furthermore, it was shown that refluxing the thiadiazole 116 in DMF (3h) gave thiadiazole-2-thione 115 via a thio-Claisen rearrangement. 

It should be noted that Trost s DPPBA-derived ligand 21 possesses considerable utility in many other situations of allylic substitution, for example with substrates which are cyclic or which possess enantiotopic leaving groups, or with prochiral nucleophiles.1171... 

By this complex formation with monomer the A1X3 is effectively deactivated. It is important to realise that these experiments not only provide convincing evidence for the initiation by ions derived from the initiator, but also an almost insuperable obstacle to Kennedy s allylic hydride theory [9] and any other theory which involves a reaction of monomer with A1X3 molecules as the initiation step. 

During the investigation of the molybdenum-catalyzed epoxidation of the allylic alcohol (43) mediated by a chiral (S)-proline derivative (44). S. Coleman-Kammula... 

In view of the Zr-catalyzed enantioslective carbomagnesation-elimination tandem reaction of allylic derivatives discussed earlier, a similar process with EtjAl might be expected and has indeed been developed recently [29]. As a representative example, the reaction of 2,5-dihydro-furan with 3 equiv. of Et3Al in the presence of (i )-(EBTHI)Zr[B[NOL-(5)] (8) and (NMTHI)ZrCpCl2 (9) produced, after hydrolysis, (S)-2-ethyl-3-buten-1 -ol in 90 and 67% yields, respectively. The enantioselectivity observed with 8 was >99% ee, whereas that observed with 9 was 85-90% ee. Upon deuterolysis of the organoaluminum products, a mixture of monodeuterated and nondeuterated products was obtained and the extent of D incorporation increased to 94% with neat Et3Al without any solvent. The results indicate that the reaction must produce two organoaluminum products, 10 and 11 (Scheme 4.18). On oxidation with 02 only... 

TABLE 4.S. Zirconium-Catalyzed Enantioselective Ethylmagnesation and Ethylalumination of Allyl Derivatives... 

S)-Proline-derived phosphoramides catalyse enantioselective allylation of aromatic aldehydes with allylic trichlorosilanes.90 Chiral a-aminoaldehydes have been allylated diastereoselectively with various reagents.91... 

---