Hydroxy protection benzyl-type groups

For a more appropriate adaptation of the benzyl-type backbone protection to the Fmoc/tBu strategy, the 2-hydroxy-4-methoxybenzyl (Hmb) group was proposed because incorporation of the 4-methoxy moiety leads to significantly enhanced acid lability.The Hmb amino acids are prepared analogously to the Hbz compounds (Section 2.3.2.1),P 1 and the AT -Fmoc-protected AT -Hmb amino acids can be obtained by reaction of the Hmb amino acids with Fmoc-OSut l or, upon silylation, with Fmoc-ClP in the presence of a base. 

The allyl alcohol (362) reacts similarly to (169) and from it the estra-pentaene (395) has been obtained with an over-all yield of 31% in two stages [459] and also the 6,7-dimethoxy analog of the carbinol (169) [499]. Vinyl carbinols of the type of (398) with a free hydroxy group (R = H) [214, 482-485, 489, 500] or with a hydroxy group protected by a tetrahydropyranyl residue (R = TP) [463,501] or by a benzyl residue (R = CH2Ph) [442, 501, 502] have also been used in the reaction with the methylcyclopentanedione (the yields in Scheme 38 are given for R = H). Similarly, (395) and (400)... 

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