NOVELTY - Preparation of (2R,6S,14S)-13-oxa-3-azahexacyclo-icosa-7,9,11-trien-11-ol derivative (I) involves reacting (11S)-17-oxapentacyclo-heptadeca-4(9),5,7-triene derivative (II) and leaving group-containing compound (III) or carbonyl group-containing compound (IV) in presence of metal catalyst.    USE - Preparation of (2R,6S,14S)-13-oxa-3-azahexacyclo-icosa-7,9,11-trien-11-ol derivative used for preparing buprenorphine (claimed), naloxone, naltrexone and nalbuphone.    ADVANTAGE - The method enables environmentally-friendly, quick, safe and economical preparation of (2R,6S,14S)-13-oxa-3-azahexacyclo-icosa-7,9,11-trien-11-ol derivative.    DETAILED DESCRIPTION - Preparation of (2R,6S,14S)-13-oxa-3-azahexacyclo-icosa-7,9,11-trien-11-ol derivative of formula (I) involves reacting (11S)-17-oxapentacyclo-heptadeca-4(9),5,7-triene derivative of formula (II) and leaving group-containing compound of formula: R2-LG (III) or carbonyl group-containing compound of formula: R6=C=O (IV) (when group (R2) is C(O)R6) in presence of metal catalyst. The preparation of (2R,6S,14S)-13-oxa-3-azahexacyclo-icosa-7,9,11-trien-11-ol derivative further involves removing group (R2) in groups (R1, R8, R8', R3, R5 and/or R4), when R1, R8 and/or R8' is H, R3 and/or R5 is OH, and/or R4 is hydroxy-substituted 1-10C alkyl.    R1=H, 1-10C alkyl, C(O)1-10C alkyl, C(O)O-1-10C alkyl or PG1;    R2=C(O)R6, C(O)OR6, S(O)R6, SO2R6, P(O)R6R6', P(O)(OR6)R6', P(O)(OR6)(OR6'), C(O)NR6R6' or C(O)SR6;    R4=H, 1-10C alkyl, C(O)1-10C alkyl, hydroxy-substituted 1-10C alkyl, or PG3-O-substituted 1-10C alkyl;    R5=OH, O-1-10C alkyl, OC(O)1-10C alkyl, OC(O)O-1-10C alkyl or OPG4;    R6,R6'=3-10C cycloalkyl, 3-10C heterocycloalkyl, 3-10C cycloalkenyl, 1-20C alkyl, 2-20C alkenyl, 2-20C alkynyl, 6-10C aryl or 5-10C heteroaryl (all optionally substituted by one or more substituent (a));    substituent (a)=R7, OR8, SiR7R7'R8, NR8R8', SR8, S(O)R7, SO2R7, halo, CN or NO2;    R7,R7'=1-6C alkyl, 6-10C aryl or 1-6C alkylene-6-10C aryl;    R8,R8'=H, PG5, 1-6C alkyl, 6-10C aryl or 1-6C alkylene-6-10C aryl;    PG1-PG5=protecting group which is removable after preparation of (2R,6S,14S)-13-oxa-3-azahexacyclo-icosa-7,9,11-trien-11-ol derivative (I);and    LG=leaving group.    An INDEPENDENT CLAIM is included for preparation of buprenorphine, which involves preparing (2R,6S,14S)-13-oxa-3-azahexacyclo-icosa-7,9,11-trien-11-ol derivative of formula I(e), treating (2R,6S,14S)-13-oxa-3-azahexacyclo-icosa-7,9,11-trien-11-ol derivative I(e) with reducing agent under conditions to provide buprenorphine, or treating (2R,6S,14S)-13-oxa-3-azahexacyclo-icosa-7,9,11-trien-11-ol derivative I(e) under deacylating conditions using alkylating reagent of formula: cyclopropyl-CH2-LG (i).