Phenylthio-l-propyne

Scheme 8 summarizes the construction of the requisite building blocks 40, 41, and 50. Alkylation of the lithio derivative of l-(tri-methylsilyl)-3-phenylthio-l-propyne (42) with 3-iodo-l-(tert-butyl-dimethylsilyloxy)propane in the presence of HMPA affords compound 43 in 90% yield. Selective desilylation of the protected alcohol is achieved by warming 43 to 40 °C in ACOH-THF-H2O... 

Cyclizations. Substituted furans are formed from HgClj-catalyzed cyclization of allenyl carbinols which are derived from 3-methoxy-l-phenylthio-l-propyne. ... 

Allene 46 is prepared from l-(phenylthio)-l-propyne 45 [37a] by deprotonation [37b] with LDA, followed by quenching with chlorotrimethylsilane (TMSCl). Hydroboration of 46 with 9-BBN leads to allylborane. The facile al-lylic rearrangement of allylic dialkylboranes allows the formation of more stable Z isomer 47. Condensation of 47 with aldehydes proceeds smoothly at room temperature, and the intermediate 48, on treatment with sulfuric acid gives the Z-diene 49 and with 4 N sodium hydroxide affords the -diene 50 (Table 24.18) [36]. 

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