Sulfoxides, 1-alkenyl aryl

Table 3. Lithiation and Subsequent Alkylation of 1-Alkenyl Aryl Sulfoxides...

In the case of 2,2-disubstituted 1-alkenyl aryl sulfoxides, lithiation leads to an equilibrium between the E- and Z-isomeric species. 

Using enantiomerically pure 1-alkenyl aryl sulfoxides ( )-(+) 6 and ( )-(-)-4> we found that 1-deprotonation and then repro-tonatlon of the ( )-(+)-4 Isomer produced no double bond isomerization and no racemization, whereas similar treatment of the ( )-( ) 6 isomer produced double bond isomerization and some racemiza-tion (eqs. 4,5) (5a). 

Likewise, the sulfoxide-metal exchange reaction of /3-acetoxy sulfoxides 164 (/3-mesyloxy sulfoxides can also be used), which are prepared from alkenyl aryl sulfoxides 163 and aromatic aldehydes, with a Grignard or alkyllithium reagent at low temperatures gives the allenes 162 in good to excellent yield (Scheme 5.24) [65],... 

The male bean weevil sex attractant has been made by a new method of allene synthesis from aldehydes and alkenyl aryl sulfoxides by sulfoxide-metal exchange as the key reaction. 

Carboxylation of lithiated vinylic sulfoxides is also highly stereoselective, as shown by a one-pot experiment leading from optically pure (if)- -alkenyl aryl sulfoxides to optically pure methyl 2-arylsulfinyl-2-alkenoates without EjZ isomerization63. 

Alkenyl aryl sulfoxides are also quent reaction with aldehydes is diasi Cyclopropanation. ° When a k< hexadiene are mixed with LDA. a tw ... 

Alkenyl aryl sulfoxides are also deprotonated at the a-carbon, and the subsequent reaction with aldehydes is diastereoselective. ... 

Lithiated allylic sulfoxides may be a-alkylated and the resulting products subjected to [2,3]-sigmatropic rearrangement induced by a thiophile to give allylic alcohols (eq 43). In contrast, alkenyl aryl sulfoxides produce a-lithiated species which are alkylated with Mel or PhCHO in good yields (eq 44). LDA has also been used to metalate allylic and propargylic selenides as weU as aryl vinyl selenides. ... 

Lithium and zinc tert-butyl phenylmethyl sulfoxide (1) and A-phenyl imines 2, in which the substituent R is alkenyl or aryl, react at —78 °C over 2 hours with high anti diastereoselection (d.r. >98.5 1.5)6. Shorter reaction times result in poorer yields, due to incomplete reaction. In contrast, the reaction of the sulfoxide anion with benzaldehyde is complete after 5 seconds, but shows poor diastereoselection. When the substituent R1 or R2 of the imine 2 is aliphatic, the substrates exhibit poor chemical reactivity and diastereoselection. The high anti diastereoselection suggests that if a chelated cyclic transition state is involved (E configuration of the imine), then the boat transition state 4 is favored over its chair counterpart 5. 

Aryl 1-Methyl-l-alkenyl Sulfoxides General Procedure31 ... 

The mode of reduction by i-PrMgCl shown in Scheme 4 and Eq. (124) was employed in stereoselective desulfurization of alkenyl and aryl sulfides, sulfoxides, or sulfones [237,314,331 Eq. (149) 314]. 

---