2- Phenylthio-l ,3-butadiene

The silicon- and sulfur-substituted 9-allyl-9-borabicyclo[3.3.1]nonane 2 is similarly prepared via the hydroboration of l-phenylthio-l-trimethylsilyl-l,2-propadiene with 9-borabicy-clo[3.3.1]nonane36. The stereochemistry indicated for the allylborane is most likely the result of thermodynamic control, since this reagent should be unstable with respect to reversible 1,3-borotropic shifts. Products of the reactions of 2 and aldehydes are easily converted inlo 2-phenylthio-l,3-butadienes via acid- or base-catalyzed Peterson eliminations. 

A stereoselective route to 2-(phenylthio)-l,3-butadienes such as 327 or 328 was developed by Pearson et al. [167] with allylboranes as crucial intermediates. Addition of 9-BBN to allenyl sulfide 324 gives the allylborane intermediate 325, which subsequently adds to aldehydes (Scheme 8.89). Typical of Peterson olefinations, this reaction can also be terminated by two different work-up procedures, either acidic conditions leading to anti-elimination, which affords Z-configuration of dienes 327, or basic work-up resulting in a syn-elimination to form (E)-dienes 328. 

Phenylthio)-l,3-butadienes (2).1 This boron compound (1) is an alternative reagent to a similar one based on titanium (11, 377) for preparation of either (E)- or (Z)-2-(phenylthio)- 1,3-butadienes (2). Thus 1 reacts with aldehydes to form adducts (a) that undergo either syn- or anti-elimination of trimethylsilane oxide. 

A different synthesis generates 2-phenylthio-l,3-butadienes directly by elimination of two molecules of thiophenol from p-phenylthio thioacetals that are readily available from the corresponding a, -unsaturated ketones (eq 48). ... 

Table 24.18 Stereoselective synthesis of 2-(phenylthio)-l,3-butadienes from aldehydes (RCHO) and allylborane 47 [36]...

Z, -2-METHOXY-l-PHENYLTHIO-l,3-BUTADIENE, 59,202 Methyl 2-(acetyloxy)benzoate, 56,63 METHYL 4-(ACETYLOXY)BENZOATE, 56,59... 

Methoxymethyl ethers, 354 (S>-< + )-2-Methoxymethylpyrrolidine, 326 (E,Z)-l-Methoxy-2-methyl-3-trimethylsilyloxy-1,3-pentadiene, 326-327 (Z)-2-Methoxy-l-(phenylthio)-l, 3-butadiene, 328... 

Z)-2-Methoxy-l-(phenylthio)-l,3-butadienes react with methyl vinyl ketone and with 2-cyclohexen-1-one under catdysis by magnesium bromide or ethylaluminum dichloride. This provides exclusively the C 0 endo adducts in which the regiochemistry is completely controlled by the sulfur substituent despite the juxtaposed influence of the OMe group, e.g. (143) (144) (Scheme 36). ... 

Methoxy-3-phenylthio-l,3-butadiene Benzene, [(2-methoxy-l-methylene-2-propenyl)thio]- (9), (60603-16-9)... 

Interesting new 1,3-dienes for the Diels-Alder reaction include (Z)-l-phenylthio-2-methoxy-l, 3-butadiene, 3 2-methoxy-3-phenylthio-l, 3-butadine, 11 and N-acyl-l-amino-1,3-butadiene 115... 

Methyl-2,5-dihydrothiophene 1-oxide in tetrahydrofuran added slowly to a well-stirred Grignard reagent prepared from bromobenzene and Mg-turnings in tetrahydrofuran, stirring continued 1 hr. at 0°, warmed to 25°, and stirred 20 hrs. at room temp. l-phenylthio-2-methyl-l,3-butadiene. Y 70%. F. e. s. D. W. Kreh and R. C. Krug, J. Org. Chem. 52, 4057 (1967). 

A synthesis of 4-alkyl-2-methoxy-1-phenylthio-1,3-butadienes by a simple -elimination of thiophenol from a thioacetal is not possible owing to skeletal rearrangement that is fostered by stabilization of a cyclopropylcarbinyl carbocation intermediate by the alkyl substituent (eq 51). Interconversion of an initial a-phenylthio carbocation to a more stable a-methoxy carbocation intermediate leads to the generation of a 4-alkyl-l-methoxy-2-phenylthio- 1,3-butadiene instead. 

Phenylthio-2-cyclopentenone, 33 a-Phenylthio ketones, 532-533 l-Phenylthio-2-methoxy-1,3-butadiene,... 

Related Reagents. 1-Acetoxy-1,3-butadiene 2-Methoxy-1,3-butadiene 2-Methoxy-3-phenylthio-1,3-butadiene 1-Methoxy-3-trimethylsilyloxy-l,3-butadiene 1 2-Trimethyl-silyloxy-1,3-butadiene. 

---