Benzyl alcohol, reaction with thiourea

Thiols. Activated benzyl alcohols are converted to the thiols by reaction with thiourea in the presence of HCl, followed by saponification. Substitution of activated aryl halides (e.g., 4-chloropyridine) is accomplished by treatment with thiourea in liquid... 

Syntheses of this type are from urea, thiourea, and amidine and guanidine derivatives. Ureas give tetrahydro-l,3,5-triazin-2-ones on reaction with a primary amine (1 equiv.) and aqueous formaldehyde (2-30 equiv.). In general, alkyl and aryl amines, unsaturated amines, amino alcohols, and a-amino esters form triazinone derivatives (Equation (43)). Methyl and benzyl have proven to be the most useful urea substituents with respect to high yields and product solubility. N,N -Dicyclohexyl- and A,A -diphenyl-urea gave poor yields of triazinone <90TL2109>. 

An important further development came from the group of Yang et al., who reported on a catalytic variant of the carbonylative annulation of benzyl alcohols (Scheme 15.14). The best results were achieved by generating the Pd-complex in situ from the reaction of Pd(OAc)2 with tetramethyl thiourea in the presence of ammonium acetate and propene oxide in tetrahydro-furan. The feasibility of Pd-thiourea as a unique catalyst has been demonstrated in the construction of a fused pyran y-lactones 45 and 46 (Scheme 15.14), the key intermediate in the total syntheses of micrandilactone A" and crisamicin A . 

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